Did you mention somewhere that the truck is paid off or almost paid off ?
Have you checked to see if you have a gps transponder connected in line with your OBD2 plug ?
Yeah, I bought it used with 123k miles on it and now have 207k.
I've continued to work on it. It's now been a year and a month or more since I started trying to repair the defect causing the C121E. So far, this is what I replaced in as close of a chronological order as I can recall:
- brake lamp switch
- All four wheel speed sensors
- front brake calipers, disks, pads, lines, flushed the brake fluid.
- brake lamp switch again.
- rear brake calipers, disks, pads, lines.
- flushed the brake lines again.
- front wheel hubs including tone rings and front wheel speed sensors (again).
- replaced the bleeder screws.
- flushed the brake lines again.
- rebuilt the ABS control module and tested it, it's working well.
- replaced the brake lamp switch again (#3).
- flushed the brake lines again.
- replaced all eight copper seal washers on the banjo bolts and replaced the bleeder screws and used thread sealer.
- flushed the brake fluid again.
- replaced the master cylinder tonight (2/22/24)..
- flushed the lines again (2/22/24) and bled the brakes twice, then performed the ABS brake bleed with AlfaOBD.
- on the test drive, I cleared the code, backed out of the driveway, put it in drive, withing ten feet, the light came back on. I cleared the code, put it in drive and it was on within ten feet. This happened five or six times and I wasn't pressing the gas or the brake. It would roll ten feet and, "bling", I'm the a-hole that thought he could fix Chysler's mistake. So, I drove it to an empty road, got it up to sixty, took my hands off of the wheel and slammed the brake as hard as I dared. Everything in the truck flew towards the windshield, the ABS pump kicked on, the truck came to a stop so fast that I went back in time, and it didn't falter and dart right or left. It stopped really, really short and was straight the entire time. Nothing locked up and nothing skidded. I did this three more times clearing the code before each attempt and watching the light taunt and mock my efforts each time by illuminating the traction control light within single digit feet of where I cleared it. I drove it to the hardware store to get some bug spray and it drove like a Chrysler that had a lot of upgrades and replacement parts. It all seemed fine, except the C121E code mocking me like the Dominoes Noid. Two days ago, I took it to have my brother-in-law take a look as he was/is a mechanic with fifty years of experience. He wasn't able to work on it because he's done enough to help me with my life and I don't want to ask for anything more, other than we took it to a parking lot and he drove it stomping the brakes repeatedly to get a feel for what it was doing. Because the brakes work really well no matter how it's stopped, whether stomping the pedal or easing it to a gentle stop, but we both noticed that if the pedal is pressed really hard after stopping, it will sink. Both of us thought it was a bypass leak in the master brake cylinder. He thought it might be the steering angle sensor or calibration because we were looking at it on the graphing feature of AlfaOBD, but that's because the readings were 0 at center, then slightly right of zero it would jump to 1433 abd decrease to 830 as it was turned right. Turning the wheel left of zero it would rise to 610. I didn't think about it then, but we were looking at the reading in the graphing feature while testing ABS module items. The next day, I connected to the steering wheel module and verified that the steering wheel is at zero when it's centered and goes to -599 when turned fully left and 601 when turned fully right. That's pretty much as dead on as I can imagine. So, I seriously doubt that the steering wheel angle is the problem.
There is no leaking fluid and everything is tight without any air getting in. I suspected air getting in so I've run about ten to twelve quarts of brake fluid through it and replaced the bleeder screws three times including using thread sealant on the most recent replacement. Also, I recently replaced every copper washer on the banjo bolts. Everything is hydraulic tight. It doesn't lose any fluid after driving it to and from work daily and I've kept a close eye on that.
I only have the brake booster and the ABS pump left to replace and that all of the brake system. I'm not spending any more on this problem because while I was attempting to repair it, I replaced anything that was worn out or not working like new. Below is all of the other items that I found that were worn and needing replacement:
- Front lower control arm ball joints replaced with Precision ball joints that have grease zurts.
- Front stabilizer bar bushings and stabilizers including bushings.
- Inner and outer tyrods.
- Front shocks with Rancho brand shocks.
- Front upper control arms with Mevotech forged control arms, ball joints with grease zurts, and bushings.
- Rear upper and lower adjustable control arms (my axle was a bit off and needed adjustable control arms to straighten).
- Rear shocks replaced with Rancho shock absorbers.
- 3" lowering springs in the rear to level the truck.
- A set of Midway tires which I highly recommend for trucks that are mainly on roadways.
- Front wheel hubs replaced with wheel hubs that have Timken bearings because I found a loose wheel when I had the tires replaced.
The suspension system is pretty much new. My alignment guy, who does an amazing job (I think he might be working out of a chop shop though) he said that I should consider changing the front lower control arms because I might have a bad bushing. I laughed because if I did, that would be everything. I asked why he thought there was a problem. He said that although he and three other guys couldn't get it to budge, one of the bushings he suspected might have a separation in it. I told him I would think about it, but not any time soon.
All of this work and all of these parts were due to the C121E fault code that is still there. I really have nothing more to give to the truck and I'bmve already gone way too far for a truck with 207k miles on it. I should have sold it because it's little crap like a dash light that is going to be on until the metal gets recycled in a scrap yard that will haunt me until I donate it to a charity that doesn't need another problem and would rather have the scrap value. This fault code will be the death of a truck because I don't want it anymore and I really don't care if there is a solution. It would have to be my only option if I get another Chrysler, Dodge, RAM or whoever designed this travesty. I've had a Ford truck, it sucked and drove like a crippled pig. I've had a GMC, but it burned to the ground, luckily three days after I sold it, but it wasnt much better before I sold it. I refuse to buy a Toyota because I was forced to drive Toyota when I worked for a former employer. I'm over 6' tall and Toyotas are not designed to fit people that tall comfortably nor are they designed for people who steer left handed. My credit is shot, so Nissan is out of the question. That leaves the bus. I'll be preferring to take the bus as my primary transportation soon. That's good though because I work for a public transit authority and I get free unlimited rides for life.