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Old 04-24-2010, 07:25 PM   #1
72gmcshorty
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Brake light on. Codes?

1992 GMC, 305, 255k. My check brake light is on. The one in the corner. It doesn't come on right away, usually after driving for a while. When i turn the truck to the on postion the light is not lit. Can i only check the code once it lights up? The PO said there was something wrong with the e-brake cable but i haven't looked. Would there be a code for that?
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Old 04-24-2010, 08:29 PM   #2
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Re: Brake light on. Codes?

It sounds like the RWAL system is turning the dash brake light on.
RWAL stands for REAR WHEEL ANTILOCK. RWAL was standard equipment starting in 1988 on full size trucks.

1988 and newer trucks of that body style that do not have 4 wheel ABS have RWAL.

There are three brightness levels of the dash brake indicator light on RWAL equipped trucks.

Brightest – park brake
Medium – Combination valve (aka metering & proportioning valve)
Dim – RWAL System

Watch the light very closely and apply the parking brake. Did the light get brighter?

When the key is first turned on the RWAL module turns the dash brake indicator light on for 2 seconds, then it should go off.

You can unplug the wire on the Combination valve to see if it is the cause on the light coming on.

The RWAL system can store trouble codes, but it is only capable of storing one code at a time.

If the light is blinking the manual states you should still check the codes by turning the key on (engine not running) and put a jumper wire between terminal A and H of the ALDL. Count the brake light flashes.

You can retrieve RWAL codes without a scan tool.

If the instrument panel light is on, to retrieve RWAL codes connect a jumper wire between terminal H and terminal A of the ALDL connector with the key on (engine not running). Watch the dash brake lamp and count the blinks. Sometimes RWAL system send out a phantom blink before the code blinks start. It can take up to 20 seconds for the code to start coming out.

Checking the code with this method can set a false code 9. Checking for a code when no code is present sets a code 9, WHICH WILL DISABLE THE RWAL system.

Clearing codes
You can clear the code by removing the power to the RWAL module for 10 seconds. Multiple circuits send power to the RWAL module and the fuses may be labeled STOP/hazard and BRAKE. Removing a fuse labeled RWAL may not clear the code. GM information on which fuse/fuses to pull is not very reliable.

The 1993 manual states to remove the STOP/HAZARD fuse.

Let me know what code or if you find a code.
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Old 04-26-2010, 06:35 PM   #3
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Re: Brake light on. Codes?

The brightness level is either dim or medium. I tested ebrake and it works. The brake light does NOT blink in the corner. It comes on after driving for about 5 mins. it will turn on steady until i turn off truck. Where is this wire i can disconnect to the combi valve thing? I guess i need to wait until the light comes on before i can check for codes.
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Old 04-26-2010, 09:12 PM   #4
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Re: Brake light on. Codes?

Quote:
It comes on after driving for about 5 mins. it will turn on steady until i turn off truck.
Look at the speed you are going when it come on and see if the light is coming on just after you reach 35 MPH.

Quote:
Where is this wire i can disconnect to the combi valve thing?
It is out by the master cylinder and has only one wire going to it.

Quote:
I guess i need to wait until the light comes on before i can check for codes.
It does sound like a soft code is being set because when you turn the truck off and restart it the light does not come on until you drive it. Try checking the code only when the light is on and see if you can retrieve a code.

Does the speedometer in the truck work well?

Do the brake lights work?
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Old 04-30-2010, 11:28 AM   #5
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Re: Brake light on. Codes?

the light only comes on after reaching 35mph.....
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Old 04-30-2010, 02:24 PM   #6
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Re: Brake light on. Codes?

Quote:
the light only comes on after reaching 35mph.....
There is a good chance that the RWAL system is setting a code 10.

On Chevrolet trucks the code 10 is for the brake light switch circuit.

Beginning in August 1990, a software change was made in the ABS controller on all General Motors RWAL equipped vehicles. The change transforms codes 6, 9 and 10 into "soft" (non-latching) codes that only illuminate the warming light as long as the fault is present. If the fault is intermittent and no longer exists, the light will go out with the next ignition cycle.

For the reason in the paragraph above I don’t think you will find a trouble code without a scanner capable of reading RWAL brake codes. Few scanners can do this.

Code 10 – Brake lamp switch circuit. Check the adjustment of your brake light switch. This code can be set by “riding the brakes” but it can also be set be driving in heavy traffic when you have your foot on the brake for an extended distance. Basically the system is detecting the brake pedal being depressed when receiving a vehicle speed sensor signal above 35MPH for what it detects as being to long of a distance.

A failing brake light switch can cause the light to come on when the vehicle reaches 35 MPH.

As these trucks are getting older, this seems to be becoming a common problem. The brake lights can work the way they should, but the brake switch, having more then one set of contacts in it, can cause problems with the RWAL system.

Even if no code 10 is stored in the system, the brake switch can cause the RWAL system to turn the dash brake light on when the truck reaches 35 MPH.

If you want to do more testing, the power comes to the brake switch from the “ECM-IGN” fuse on the pink wire with a black tracer. It should exit the switch on the purple wire. The power should go through the switch when the Brake pedal is NOT pushed (a Normally closed switch) all the way back to terminal F of the 6 wire connector of the brake control module, which is the terminal at one end of the connector with a Purple wire to it. With the key on, and the brake pedal NOT pushed, there should be power there.

Brake Switch adjustment
Here is how the switch is adjusted:
On the curved side of the switch, which is pointing down and somewhat towards the front of the vehicle when installed, the end of a lever protrudes slightly out of a slot.
While holding the brake pedal down a little ways, slide the lever that protrudes from the slot toward the driver’s seat.
Let go of the lever, then return the brake pedal to its fully released position, and the switch should self adjust.

Brake Switch mounting – Installing:
The body of the brake switch should not move with the pedal at all. When you have the switch removed look at the side of the switch that would be towards the parking brake pedal if the switch were still installed. There is a protrusion on the switch that must slide into an opening where the switch mounts. Somewhat like a big square lug into a slot.
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Old 05-27-2010, 06:34 PM   #7
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Re: Brake light on. Codes?

I am beginning to think it is the brake switch. I was driving one day in traffic and the light in the corner started to blink. I counted 10 blinks and then pause, 10 blink pause, etc. I turned off truck started up again and then light came on steady again after 35mph. It hasn't blinked again. I was also wondering if the brake light comes on if your brake pads are wearing low? Do these trucks have a sensor to detect brake wear?
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Old 05-27-2010, 08:57 PM   #8
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Re: Brake light on. Codes?

Quote:
I was driving one day in traffic and the light in the corner started to blink. I counted 10 blinks and then pause, 10 blink pause, etc. I turned off truck started up again and then light came on steady again after 35mph. It hasn't blinked again.
Replace the brake switch.

Brake Switch mounting – Installing:
The body of the brake switch should not move with the pedal at all. When you have the switch removed look at the side of the switch that would be towards the parking brake pedal if the switch were still installed. There is a protrusion on the switch that must slide into an opening where the switch mounts. Somewhat like a big square lug into a slot.

Here is how the switch is adjusted:
On the curved side of the switch, which is pointing down and somewhat towards the front of the vehicle when installed, the end of a lever protrudes slightly out of a slot.
While holding the brake pedal down a little ways, slide the lever that protrudes from the slot toward the driver’s seat.
Let go of the lever, then return the brake pedal to its fully released position, and the switch should self adjust.


Quote:
I was also wondering if the brake light comes on if your brake pads are wearing low? Do these trucks have a sensor to detect brake wear?
No, and No!
The wear sensor in not electronic. It is just a tab that hits the rotor and makes noise.
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Old 06-09-2010, 07:48 AM   #9
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Re: Brake light on. Codes?

While we're on this subject
My Brake/Park brake light came on the other day
It comes on and stays on right from turning the key on
There doesn't seem to be any change in braking capability
This light being on really worries me (am I going to have any on my next app??)
Oh yeah,'90 5.7 3 sp w/od 1/2 ton
ps ALDL?
Thanks T
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Old 06-09-2010, 08:25 AM   #10
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Re: Brake light on. Codes?

Just started my truck to go to work
Yes, the warning light gets brighter when the E brake is applied,
my daytime running light indicator also goes out
T
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Old 06-09-2010, 08:52 AM   #11
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Re: Brake light on. Codes?

Quote:
Originally Posted by 63sbssbbw View Post
ps ALDL?
Thanks T
ALDL connector

ALDL (Assembly Line Diagnostic Link)
Also referred to as the DLC (Data Link Connector)


There is a photo of an ALDL at this site:
http://www.aldlcable.com/

More links:
http://robertpowersmotorsports.frees.../ALDL_plug.jpg

http://autorepair.about.com/library/images/bl428lib.htm



Quote:
Originally Posted by 63sbssbbw
my daytime running light indicator also goes
I have never seen a truck that old in the United States with daytime running lights.
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Old 06-10-2010, 07:06 AM   #12
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Re: Brake light on. Codes?

Thank you Chevytech
I would've called it an obd1 port
Please excuse my ignorance,as,believe it or not,this is the newest vehicle I've ever owned
Drove an '89 f250(in my sig)for about 10 yrs and before that drove early G bodies('78s).
i vowed for a long time not to own anything with a computer in it,but as we know, we all have to catch up sometime(the fact that I'm typing this,right here,right now is proof of that).
I really appreciate the help and insight you guys put out there.
As far as daytimers go,it could be a canadian thing?
Anyway,back on topic.
I've had this truck for about 2 months, just trying to get it daily driver worthy,already done basic stuff,tune up ,replace leaky PS hose etc.
When I brake hard should I be able to feel the ABS even though it's only in the rear?
Will be tearing into it this WE to check mechanical aspects to eliminate that from the equation(Because I can LOL).
I also noticed that my brake fluid is pretty dirty,Could this be an underlying problem?
Even if it isn't I'd like to flush it anyway
Thanks again
T
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Old 06-10-2010, 10:41 AM   #13
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Re: Brake light on. Codes?

Quote:
Originally Posted by 63sbssbbw View Post
......As far as daytimers go,it could be a canadian thing?......T

I recall that Canada began the DRL thing back in the mid-60's. Seems that the first ones were an auxillary light that came on with the ignition. My mental image is of a Chrysler product with that additional light mounted to the grille...kinda like using one of the Mustang GT fog lights....at the time.
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Old 06-10-2010, 10:27 PM   #14
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Re: Brake light on. Codes?

Quote:
Thank you Chevytech
You’re welcome.

Quote:
I would've called it an obd1 port
With many years spent in the dealership I usually use the terminology that GM uses in their publications.

Quote:
When I brake hard should I be able to feel the ABS even though it's only in the rear?
No.
It is not easy to feel. I have done a skid on dry pavement and activated the RWAL, and felt it, but it is not as noticeable as most antilock systems.

Quote:
I also noticed that my brake fluid is pretty dirty,Could this be an underlying problem?
It is possible for dirt to cause problems in the isolation/dump valve.
Get the code out and see what is going on, or see if it is the combination valve turning the light on.

More information on doing these tasks can be found searching my username and RWAL.
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Old 06-11-2010, 07:20 AM   #15
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Re: Brake light on. Codes?

Thanks again CT
When I first got the truck I visited this section (door hinge pins)and spied a link for CFM technologies and put it in my favs for future reference,Pretty sure it was from you (or Chevloray)Thanks for that,kinda like getting tools for xmas LOL
I will try to get the codes tomorrow
In fact,I think I'll do that FIRST,as it may save me some unnecessary work.
As for the RWAL, I did a little test on the way to work yesterday (6 mi out of town,so no traffic),I hauled it down to a stop from about 55 mph, I could just slightly feel RWAL,but I could feel it more in the truck itself rather than in the pedal.
I was also prepared for the fronts to lock up, but they didn't.
As for DRL Ray,My '89 f250 doesn't have them
T
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Old 06-11-2010, 09:40 AM   #16
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Re: Brake light on. Codes?

This thread is the bomb for RWAL issues. ChevyTech is the man in the know and I appreciate him sharing his knowledge. He doesn't get paid for that, but is kind enough to provide the info.

As for the DRL's in Canada, like I said I remember seeing an article back in the mid-sixties, that had something about it. I also remember that it seemed that the cars with Canadien plates had DRL's, when US-tagged cars did not.

It ain't no show stopper, but is something that got stuck in my brain and one of the comments on this thread just brought it out.

I run the DRL's on my truck, for safety, but I disabled them when my son was in the USAF, because they want you to turn off your headlights when you enter the gates. When he and I traded, the fuse went back in and the DRL's came back to life. The heat from the bulb keeps the condensation out of the headlights (but that's another topic).
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Old 06-12-2010, 05:31 AM   #17
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Re: Brake light on. Codes?

Did my code read after work yesterday
using a paperclip I bridged A and H
Got a code 9,I let let it go at least 15 times and still code 9
Removed paperclip
it still flashed code 9
turned ign off
turned ign to run,still flashed code 9(with no paperclip)
started truck,still flashed code 9
shut truck off,turned ign to run
disconnected the one wire combi valve wire and reconnected it
still flashed code 9
This drove me nuts
Unhooked and reconnected the pos battery cable
Now my brake warning light is not on
Does the original problem still exist?
Have I just put virtual "tape over the warnig light"?
I also noticed after all this that the brake warnig light does not come on for 2 seconds at start up
Have I disabled my rwal?
I agree Ray ,if we still ran rep points CT would certainly be getting some from me
You also have plenty of good stuff that i've read
Heck, this whole site(and the people in it) is the bomb.
Thank you CT
Trent
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Old 06-12-2010, 11:58 AM   #18
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Re: Brake light on. Codes?

Checking for a code, by jumping the ALDL terminals, when no code is present sets a code 9, WHICH WILL DISABLE THE RWAL system.

Code 9 = High resistance or open speed sensor circuit (resistance should be 1000 to 2500 ohms)

Beginning in August 1990, a software change was made in the ABS controller on all General Motors RWAL equipped vehicles. The change transforms codes 6, 9 and 10 into "soft" (non-latching) codes that only illuminate the warming light as long as the fault is present. If the fault is intermittent and no longer exists, the light will go out with the next ignition cycle.

If the vehicle has a speed sensor problem it will turn the light back on. If the speedometer does not work at times or the service engine light is coming on setting a code 24, then you need to diagnose the speed sensor circuit.
Quote:
Unhooked and reconnected the pos battery cable
Now my brake warning light is not on
This should clear the code so the system will function again.

Quote:
Does the original problem still exist?
If there is a problem the light should come back on. Drive the vehicle and see if the light comes back on.

Quote:
I also noticed after all this that the brake warnig light does not come on for 2 seconds at start up
Have I disabled my rwal?
The system is designed to run a self test at start-up. If it is not turn the light on for two seconds it could have a bad RWAL module.
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Old 06-12-2010, 06:22 PM   #19
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Re: Brake light on. Codes?

Thank you CT
It did not light up when I left work yesterday,which was the initial start after reconnecting the battery
went to work this a.m. and DO have the 2 second light, at run and after start up
As for the DISABLing THE RWAL,I was really just looking for affirmation that I understood.
A little off topic,but maybe not
I read a thread in general discussion this morning about hyjacking threads(and I agree with the OP)
I hope I have not done that here,hopefully 72gmcshorty gets his brake like issue sorted out,if not, I'm sure he'll be back to this thread for more help.
Even in a search,finding 2 or 3 thorough threads is better than trying to sift through 59 vague ones
IMHO
Thanks again CT,you have put my mind at ease
Trent.
.
.
NEXT!
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Old 06-12-2010, 08:12 PM   #20
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Re: Brake light on. Codes?

You’re welcome!

Starting a new thread is almost always better then hijacking or tacking onto another thread. Some threads get to be several pages long when working with just one problem vehicle. I have notice if a thread gets long people will skim it, instead of reading it, and miss important information.

If I was in the middle of a discussion with 72gmcshorty, with fast interaction, I would have ignored your question or asked you to start a new thread. It seemed like the discussion with 72gmcshorty was concluding so I thought it would be ok if I answered your question.

Short concise threads that work to a conclusion with and explanation of what problem was found are the most helpful for other people doing a search on a specific topic.

Several people have thanked me in private messages because they have found the answers to their questions doing a search, and have fixed their vehicle without have to post a question on the board and wait for replies.
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Old 02-17-2011, 12:04 PM   #21
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Re: Brake light on. Codes?

I am having a similar issue with my '90 K-5 Blazer 350 motor, auto tranny, 35" mud tires, I hit 35 mph and the brake light comes on (medium, not bright but not dim). Anyway I replaced the brake switch (now I have cruise) , cruise control stick, speed sensor, 7 plug trailer plug, checked all the bulbs, all new calipers and pads, flushed the system, switched out the ABS module. I jumped pins A to H and I believe the count was 1 long 9 short (the light was blinking fast each time I did it). Anyway disconnected the battery and the light still comes on @ 35mph and goes out when I shut the truck off again. Last night I disconnected the 6 pin connector that goes to the module and no brake warning light when I reach 35 mph. I still have cruise and a parking brake warning light when I depress the parking brake pedal.
I am at a total loss on what is going on with this light, I like challenges but this one has me stumped! Any idea's anyone?
Thank you

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Old 02-17-2011, 06:52 PM   #22
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Re: Brake light on. Codes?

Code 10 can be set by “riding the brakes” but it can also be set be driving in heavy traffic when you have your foot on the brake for an extended distance. Basically the system is detecting the brake pedal being depressed when receiving a vehicle speed sensor signal above 35MPH for what it detects as being to long of a distance.

Edit:
ASEASIDER’s truck is a square body R/V body style which has a different brake switch configuration then the newer C/K trucks.

The brake switch adjustment I posted is not for his truck.
End edit:


If this does not take care of the code 10, look at post #6 above in this thread, for more testing information. Test the voltage on the wires.
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Last edited by ChevyTech; 02-18-2011 at 08:37 PM. Reason: Different body style truck - mismatched info
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Old 02-17-2011, 09:01 PM   #23
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Re: Brake light on. Codes?

Chevy Tech,
I will verify the brake switch setting and get back with you. I basically installed it the same way I removed it (wires up) and adjusted it so when I depressed the pedal about1/8th " the light would come on. Make sence how you explained it to me.
Thank you
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Old 02-18-2011, 05:43 AM   #24
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Re: Brake light on. Codes?

GREAT thread!!
I started same thread, but mine didnt get into such great detail about how to go about fixing the problem,

MUCH THANKS for the info!
5 star rated thread!
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FAQ INDEX Thread
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Old 02-18-2011, 11:08 AM   #25
ChevyTech
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Re: Brake light on. Codes?

Quote:
Originally Posted by Mr79C10 View Post
GREAT thread!!
I started same thread, but mine didnt get into such great detail about how to go about fixing the problem,

MUCH THANKS for the info!
5 star rated thread!
Thank you!

This thread is one of the links I listed up in the FAQs sticky.

Being this thread is getting viewed so many times I am going to add some more information that has not been asked for but may help people repair their vehicles.

Codes for Dodge RWAL, Ford RABS and GM RWAL applications are similar but have a few differences:
1. Should not occur (replace the controller if it does)
2. Open isolation valve circuit or defective ABS module
3. Open dump valve circuit or defective ABS module
4. Grounded or closed RABS or RWAL valve switch
5. Excessive actuations of dump valve during ABS braking
6. Erratic speed sensor signal
7. Shorted isolation valve or defective ABS module
8. Shorted dump valve or defective ABS module
9. High resistance or open speed sensor circuit (resistance should be 1000 to 2500 ohms)
10. Low speed sensor resistance (Dodge & Ford only). On Chevrolet trucks the code 10 is for the brake light switch circuit.
11. Open speed sensor circuit (GM only) 1993 manual states this is a invalid code.
12. Stop lamp switch circuit (Dodge & Ford)
13. ABS module speed processor (Dodge & Ford only)
14. ABS module program (Dodge & Ford only)
15. ABS module RAM memory failure (Dodge & Ford)

Beginning in August 1990 (this date does not match in all information on when the change took place), a change was made to the RWAL module on all General Motors vehicles. The change transforms codes 6, 9 and 10 into "soft" (non-latching) codes that only illuminate the warming light as long as the fault is occurring. If the fault is intermittent and no longer exists, the light will go out with the next ignition cycle.
The diagnostic procedures for the code 6, 9 and 10 remains the same.
A scan tool can be used on the newer GM applications to read any soft (non-latching) codes.

On the modules built after Aug 1990 grounding the "H" terminal on the ALDL connector erases soft codes.
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Last edited by ChevyTech; 02-18-2011 at 08:46 PM. Reason: Add more for people using sticky
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