External triggering of the CEL?

[JayArr]

Hi All

Is there any way to link into the PCM so that an external piece of equipment can cause a CEL?

I'm towing a trailer and I'd like to put a "Tire Pressure Monitoring System" TPMS, on the trailer tires. most systems have you put the monitor on the dash or stuck in the inside corner of your windshield. I'd like to bury it in the glove box and have it "throw a code" if there is a problem. You can set these things so that they "alarm" on over or under pressure or temperature, I want to just set the alarms for 5psi under and forget it, I have zero interest in looking at my tire pressures while I drive.

I think it might beep but if the CEL lamp on the dash could also come on that would be neat. Are there any "spare" circuits on the PCM I can tire into?

JayArr

 

[Mooseman]

The CEL activation is tied to powertrain error codes. Not all codes trigger the CEL. In HPTuners, each code can have the CEL turn on or not when triggered. The PCM sends a signal to the cluster to turn it on when triggered and IIRC, is a separate wire from the PCM to the cluster. I supposed you could tap into that signal wire to trigger the CEL. Not sure how you could get the signal from the aftermarket TPMS system.

 

[JayArr]

Actually getting the signal from the TPMS system is pretty easy, I can get a signal from the piezo buzzer that goes off when one of the sensors creates an alarm. I can couple it to the PCM with an opto to isolate it as well.

I'm thinking that all the PCMs are the same before they are programmed right? So they start as a blank computer and the inputs are assigned to different sensors and then the programming sets a PXXX code if that input goes high or low based on the sensor.

I wonder if anyone has ever figured out all the inputs and outputs, there may be an input leftover on an Envoy PCM that was only used on the V8. Let's say the V8 has a sensor that detects Bank2 oxygen sensor 2 which is not used on the LL8, if I tied the TPMS into that line I maybe I could create an error code when the TPMS has an alarm.

The code is irrelevant, the manual/reader would identify it as a code for something that doesn't even exist on my chassis but if I can go into HPTuners and set that code to turn on the CEL then I have a light on my cluster to indicate an aftermarket system has an alarm.

 

[Mooseman]

Not sure about how you want to do but the V8 and I6 PCMs are totally different. Even if you could find an empty pin on the PCM and a fake code, what value would trigger it? Even HPTuners can just manipulate stock tunes so if something doesn't exist, it can't change it. Just sounds like an overly complicated way to get a light. I'd be looking at just having an LED come on on the dash. There's even red and blue flashing ones.