Intermittent left rear ABS sensor not sending signal?

Thermostat rationality code.

Steve,

Yes, there is a "glitch" on the dash. But it is accompanied by a dinging when the rear park sensors are "off". This is new, it was just dinging 1 time and then telling me the sensors are off. It only has done this off/on "glitch" 2 times.

Should I replace the thermostat?

I have another appointment with my local dealer on Monday. I have all the history and videos to show them. Hoping they can figure it out.

He didn’t tell me what color wire he fixed.

I’ve flushed my heater core and replaced the coolant but struggled some to bleed it. Is there a link to a process? I have a closed system.

Due to rain, I have been unable to try any of the evaluations you have recommended. I have tendered my truck to my local dealer to hopefully complete these repairs.

Update:

1) Thermostat replaced and no further problems

2) Right taillight and back up light - found the "repaired" wire which the dealer stated was only taped and not repaired. Repaired this broken wire free of charge and taillight works as does back up light. On a side note, the original call back about the backup light was that "I needed a new bulb" and I had to correct them that I checked the bulb, and it was intact.

3) Rear Park sensors - those intermittent warnings have resolved once the above wire was repaired.

4) ABS sensor - through their testing the line, the sensor, driving, watching the active and stored codes they believe I have to replace my rear axle housing as this will give me a new bolt hole to secure the sensor. They state the sensor is not secure nor square with the speed ring and thus the bumps cause erratic reading and codes. They found no HCU or ABS module codes. This is a quoted $4500 repair on an 8-year-old truck with 129,000 miles.

My response is to have them check the original sensor I had in when this all began, I still have this sensor. If it is good, I believe I'll take a chance and still change the HCU and ABS module. I am basing this on all the reports I have read on talk forums with trucks just like mine having the same issue => no HCU/ABS codes, many sensor changes, new line run to the sensor, and no fix until these modules are changed. I realize it is a risk but I believe its a better risk as I cannot get the dealer to guarantee their recommendation will be the fix.

Any and all thoughts are welcome. I am ignorant but trying to assimilate all the information I am getting.

It's not the sensor hole, it's the bolt hole. They think since it's "off" it makes the sensor sit crooked and move in the sensor hole.

Steve, exactly my thoughts but I don’t have the experience to be confident.

I’ve decided I’m going to replace the HCU and ABS module and see what happens.

So, I had the dealer check the original Mopar sensor thinking if it worked well then, the original intermittent signal was not from the sensor. They told me the original sensor didn't give signal and as such didn't work. So, I was back to wondering which repair to perform. I decided to replace the ABS module and HCU. My buddy and I could do this and see what happens. I bought the parts yesterday and a scanner from AutoZone that could bleed the ABS. I drove 1.5 hours to my buddy's shop, and we got started. Now, he is a heavy equipment mechanic working on dozers, skidders, loaders, etc, mainly John Deere. We decided to start over, and he called his Snap-On rep who used to be a Mopar mechanic. He told us the problem was the line rubs through somewhere and to run a new line. It is a twisted pair, and my buddy should know how to do this secondary to his experience with John Deere. We decided to check the line to confirm. We put the reader on it and line 41 showed 3.7 ohms/milliohms and line 42 showed 25. My buddy laughed at all the trouble I've had for 3 months. Now, to back up, this confirms what my neighbor and I found early in the process when we couldn't get continuity on line 42 but could on 41. We got confused when we broke the line at the 12-pin connector and had good continuity on each segment of line when they were broken at the connector. So, my buddy twisted a new run, and we spliced it in. All dash lights off. I drove the truck the 1.5 hours home, hitting holes and sparing no speed/line to ensure the truck bounced around. I had no problems. I ran the cruise control, in and out of 4wd and 4 low. Today I went to our favorite swimming hole down a rough logging road and had no problems. Had to use 4wd even. So, a new line seems to have fixed it.

I asked the dealer if they had tested this line and they said yes.

My rear sensor problem and right taillight out warning showed up again after we completed the repair. I tackled this this morning as I had noted the repair by the dealer just before the large connector at the back of the front wheel well yesterday. What I found was one of the locking tabs on that connector was broken. This didn't allow the connection to seat or be square once the lock was engaged. I ensured the connection was in and square and locked. Then I zip tied the top and bottom of the connector careful not to pinch any wires. This alleviated the taillight and rear park sensor problem. I went to my local shop, where I get my tires as well, and they cleared all the stored codes.

So, I believe I have all my problems resolved. I now know more about testing 12-volt connections.

Thank you for all your advice and direction.