LFD2037

I tapped 2 new license plate lights into my 4 way running lights wire 'cause I got a new bumper. I noticed my left brake & turn were not working. So I unhooked the new lights. Turned it on/off/on/off w/no change. Checked fuses & the one for left brake/turn was blown. Then the left worked but not the right. So I got the Smarty & returned truck back to stock. Then when I turned the truck back to run(not started), after returning it to stock, the speedo & RPM gauge swing all the way to the max(right), the time on the clock went to 12:00, the overhead went to 15 MPG from 18 MPG & the ABS light stays on. Checked DTC's & it said PC121 'unknown code'. I checked fuses again & I didn't put the one for the right turn/brake back in. ALL lights work fine now. So then, I reloaded Smarty update & the code was still there. I erased it 3 times & it comes instantly back. What does this code mean(it's not on the WIKI list), why is the ABS light on & why won't it go away? If it's an ABS code, do they get erased by the Smarty when it says 'erasing DTC'? I'm kinda freaking out here. TIA

tritont

I believe your code is a P0121. Don't know why a bad TPS would cause problems with your lights though.

P0121 - TPS/Pedal Position Sensor A CKT Range/Perf

LFD2037

I looked again & it's not P0121. It says PC121. My speedo doesn't work, e-brake light stays on & ABS stays on.

tritont

Well then, you're right. I just looked through all the codes in the service manual and that's not one of them... for the ECM anyway. It may be a PCM code then. I'm still lookin but, don't see anything for it yet.

tritont

well, I couldn't find anything starting with PC. I did find this though which may help somehow... look at #4 about the relearn function. Don't know what to tell you ??

NOTE: 1. After completing the Powertrain Verification Test the Transmission Verification Test must be performed.
NOTE: 2. If the PCM has been replaced and the correct VIN and mileage have not been programmed, a DTC
will set in the ABS Module, Airbag Module and the SKIM/SKREEM.
NOTE: 3. If the vehicle is equipped with a Sentry Key Remote Entry, Secret Key data must be updated. Refer
to the Service Information for the PCM, SKIM/SKREEM and the Transponder (ignition key) for programming
information. Using the scan tool, program the Secret Key information into the PCM using the PCM replaced
function under the WCM menu.
NOTE: 4. If this vehicle is equipped with an Electronic Throttle Control system, and the APP Sensors, PCM,
or Throttle Body Assembly have been replaced, use the scan tool to perform the ETC RELEARN function.
NOTE: 5. When replacing an O2 Sensor, the PCM RAM memory must be cleared, either by disconnecting the
PCM C1 connector or momentarily disconnecting the Battery negative terminal

LFD2037

I appreciate your help. Hopefully Bob or Marco will chime in. Is an ABS code & a DTC the same type 'codes'? On Mads site is says 'Erases ABS codes also but does not display them'. How do I do that?

Bob Wagner

your short circuit may have cause a tipm issue that the dealer may have to address.

LFD2037

Bob, What is a TIPM issue? How do I erase abs codes? Thanks for your support. It's pricele$$ !!

vzdude

Humor me if you have a minute.......hold the trip odo button then turn the key on . The instrument cluster should go thru some test and may show a code. After that, shut the key off again, and try retrieving the code with the key trick.....turn key from off to on 3 times ending in the on position. Codes will read out in the odo screen.

tritont

" Totally integrated power module " IIRC, it controls the voltage sent to the light. If you're drawing too much current, it may have caused the code. I've seen this before when people try to connect extra trailer lights.

Disconnect the lights you hooked up and see if that helps. If it does, you likely need a resistor inline with the lights.

vzdude

That's what a bulb is.....additional resistance. Adding a resistor will only make it worse ....IF that is what the code is for. I don't think it is though?

tritont

It will need a resistor to fool the TIPM into thinking there is no extra voltage being drawn. resistor may not be the right thing but, I bet it's the right track.

It's pretty hard for the Smarty to cause ECM issues.

vzdude

Oh....I don't think it's the Smarty either, just wanna figure out what code it is for sure. But really.......adding the resistor will only make it worse. There is a TIPM reflash to help with the lighting trouble. The higher the resistance, the higher amperage draw is on a circuit. That is what the TIPM is looking at....amperage. The reflash makes the limits a little higher to eliminate that trouble.

LFD2037

With the trip check it showed; 5 121 & , 282 & 5 447. The key 3x's trick showed; U 0121. I've never seen it show a U but I have seen it show a P. I did unplug the lights about 1 min. after I plugged them in.

tritont

right you are . resistor was from lack of a better term. I'm used to dealing with high voltage so resistors aren't my thing :-)