My Check Engine light is lit on my '99 Ram 2500. I've checked the DTC's and there are none (using Autotap via my laptop). The truck runs great - well, it does now that I've replaced the plenum plate/gasket and rerouted the spark plug wires per the TSB's (lol). I can find nothing wrong with the vehicle. Runs great and shows no DTC's. Seems to me that the driver transistor/chip for the check engine light is probably shorted/bad. Does anyone know which connector and pin number on the truck's computer this would be? I don't want to replace the ECM but the light is driving me crazy. Also, does anyone have any experience with repair of these units?

 

In the DIY/FAQ section, you can download the 01 service manual. It will have detailed wiring diagrams, and connector pinouts for you.

Is the light on solid? Blinking?

 

When you fixed the plenum, did you address the related problems with the o2 sensor and the cat? Try checking the codes in this manner. https://dodgeforum.com/forum/2nd-gen...code-list.html And look through the FAQ/DIY section(which you should do anyway), you can download a 2001 FSM that has wiring diagrams in it.

 

Thanks for the replys! First off, yes the check engine light is on solid. And, I cannot clear it. Unless, of course, it actually is clearing and then immediately coming back on. In any case, it's on solid all the time.

At this point, I have only done the plenum fix and rerouted the spark plug wires. I had Hughes send me an O2 sensor along with the kit, but have not installed it yet. I was still mulling over in my mind whether I should go ahead and use some top engine cleaner before replacing the O2 sensor. Any suggestions or experience with this? Also, I haven't even thought about the catalytic converter being an issue.

Could the ECM turn on the check engine light without setting a DTC? Possibly from the plenum issue. I can tell you that the engine ran like crap before I pulled the intake manifold. Now it runs like a top. I drove across town and back yesterday after filling up and the fuel gauge never left the pegged high position. Before, it would have dropped about a quarter tank!

 

Plenum problem won't in and of itself set a code, leave it go too long, and other problems start occurring, that MIGHT set a code.....

Run some SeaFoam thru a vacuum line with the engine running. Just let it suck it in. (have to hold the idle up a bit, else it stalls.....)

If the light is on solid, and your scanner is communicating with the PCM, I would suspect either a PCM problem, or, a problem in the cluster......

The PCM should have a data point somewhere for the MIL, or CEL being on. See what that says.....

 

I'm wondering if anyone knows of the Check Engine light being lit without any code being set in the PCM. I've always thought that the PCM would set a code if the light were lit. However, I'm using the AutoTap program on my laptop and only purchased the 'generic' monitoring software (they sold, at the time of purchase, an extended set of monitored parameters - for more money, or course). I'm wondering if the software I'm using may be fooling me into believing that it's the instrument cluster. Anyone have any experience with this. Do the transmission DTC's go through the PCM? Thanks for any help!

 

PCM controls Trans too, and your scan software should get them as well. PCM suggests to the instrument cluster when to turn the light on...... so, it may be a fault with the cluster, or, it may be a fault with the PCM. No idea how to figger out which, aside from replacing one or the other, and see if the problem goes away.

 

Did you try the key trick in the link I gave you?

 

I tried the Key-On-Off trick per the link, but got nothing. My Dodge RAM is a '99 and, near as I can tell, that trick only works up through '97. I'm kinda believing it's the instrument cluster causing the problem. I just don't have the money to swap out the instrument cluster and the PCM to determine which is the problem. I wish there was a way to pinpoint the failure without having to go that route. Thanks for all the replys!

 

What we really need is a PDF copy of the diagnostics manual....... its a separate book from the service manual......