DTC help!
 

So I've got an '85 Suburban with a 5.3 in it from an 04 Avalanche. Completed the swap about 2 years ago and it's been great. This morning on my way to work I noticed the RPM's felt a little high going 80, so I did a system check with my Blue Driver device and came back with 3 DTC's...

P0101 - Mass or Volume Air Flow Sensor "A" Circuit Range/Performance

P0654 - Engine RPM Output Circuit/Open

P0724 - Brake Switch "B" Circuit High


I've done a very little amount of quick research and the last two possibly point to a bad PCM (it's from an '03 Silverado from a salvage yard), possibly bad brake switch, possibly a bad connection at the PCM or bad wiring?
First one may be bad mass air flow sensor?

Just looking for advice or input on what I can do/check or what common fixes are. Any help is greatly appreciated!

Re: DTC help!
 

I would check all of your fuses related to the swap. I wouldn't jump to the conclusion the PCM is bad.
Also check your grounds, if they have gotten loose they can play havoc on things.
Dave

Re: DTC help!
 

The brake circuit switch will take you out of lockup on the highway, which is probably why your're feeling increased RPM.

Re: DTC help!
 

I will check fuses on my break here shortly. I agree and will check grounds too, I've heard way too many stories about crazy weird electrical problems being due to a bad ground. I think I have 1 from engine to frame, 1 from engine to body and 1 directly from battery to frame....should I have more than what I currently have?


That's exactly what I was thinking too.

Re: DTC help!
 

You need to check your engine harness grounds, there are usually three of them on a truck harness.

Re: DTC help!
 

Thank you for the heads up on there usually being 3 of them, I will absolutely check that out!

Re: DTC help!
 

Do you have a tach hooked up?

Re: DTC help!
 

The mass airflow code could be a huge number of things, dirty maf, vacuum leak, leak in the air intake tube after the maf, fuse, bad ground.

The TCC code means that the PCM is detecting 12v all the time on the TCC brake switch line. It shouldnt keep the torque convertor from locking up since the PCM should ignore the brake switch functionality all toghether if either of the two codes for it are set. The torque convertor will just unlock below the set speed not when you hit the brakes. Can't imagine a bad fuse or ground could be causing this one.

The engine speed code is the same one that is always set in my swaps if the customer doesn't hook up a tach to the tach wire.

The TCC code and the engine speed code aren't aeven severe enough to set a check engine light. I would focus on the MAF code. If fuses and grounds are good get some MAF cleaner. Those things are notorious for getting dirty really easy.

Re: DTC help!
 

I do not have a tach hooked up, should I? I've been using my Blue Driver device for my gauges....



I do have 3 grounds off the engine. I went through and cleaned 1 up and re connected it, 1 is good and the last one looks good but I'm going to take it apart and clean it just for piece of mind. I've been driving it since then and the only code that comes back is the P0654 code. Would hooking up the tach wire help this?

Just for piece of mind I did go through and clean the mass air flow sensor and re-installed it making sure all connections to and from it are good as well as the intake tube to the throttle body. And thank you guys big time for all the help with this so far! I've learned something from this for sure, it helps!!

Re: DTC help!
 

hooking up the tach wire would likely get rid of the code, though it doesn't really matter. having the code set won't affect anything.