2007 HSE HD - 4.4L - 175k miles
Atlantic British coil conversion kit with hardwired module

The brake light came on and I get a bong with "system fault special programs not available" on start up. I pulled these codes:

• P0504-64 (2A) Brake switch A/B correlation - Algorithm based failure - signal plausibility failure
• P0504-29 (2A) Brake switch A/B correlation - General signal failure - signal is invalid
• C1A02-94 (2E) Rotary encoder stuck in the intermediate position - Component failure - unexpected operation

Steps taken:

• the original terrain selector unit had corrosion on the rotary switch, so I replaced the whole board with a used one from a 2007 L322 as the boards look identical and have the same part number stamped on them
• checked brake light bulbs, all working, all P21/5 bulbs
• replaced the brake light switch, cleared codes with my GAP tool
• brake light switch red wire measures 12v
• checked ground connections in both footwells and under the driver's side dash (LHD) with nothing seemingly out of place or corroded. A likely splice culprit on the passenger side has already been addressed, so that was a pleasant find
• wheel speed sensors show correct live data, so I don't think they're to blame for remaining symptoms, despite it feeling speed-related

Remaining symptoms and codes:

• P0504-29 and P0504-64 come back but with no CEL
• I still get the bong and "special programs unavailable" on the display whenever I come to a stop. It doesn't matter if I brake or just roll to a stop. It also happens when transitioning from reverse to drive and vice-versa
• Despite that messaging, terrain modes are confirmed working (throttle response noticeably changes, display shows/changes terrain icons, hi/lo works)
• no cruise control
• while moving, I can clear the codes and temporarily restore cruise control until I come to a stop and get the above behavior again

What else should I be checking? What am I missing here? Thanks in advance for the help!

 

No cruise control and a rotary encoder fault makes me think of the clock spring in the steering wheel. That for sure will prevent the cruise control from working.

Jeff

 

Thanks for the insight! When in park, I can control my GAP tool with the cruise control buttons which makes me think it's not the clockspring. I just realized I haven't checked the TCM and connectors (behind the battery) for corrosion. That's my next task. I'll report back with findings.

 

Definitely made sure to put the brake switch back in the same orientation as the old one? Basically, the plunger is aligned the right way, etc. When I did my brake switch for the first time, I put it back rotated 180* (plunger on wrong side) and it spit all kinds of errors at me. Flipped it and made sure it was sitting in the correct space and fully seated and the errors went away.

 

Do you have trailer wiring and or have you looked for some bad trailer wiring job done up behind the rear access panel inside?

 

The book says:

C1A02- 94 Rotary Encoder Stuck In Intermediate Position - Unexpected operation
The terrain response switchpack is held in an intermediate position (between the special programmes) for more than 60 seconds Foreign object preventing correct operation of terrain response switchpack Mechanical damage to the terrain response switchpack

NOTE: Suspect driver error do not replace the terrain response switchpack Check for foreign object preventing correct operation of terrain response switchpack.
Start the vehicle engine, rotate the terrain response switchpack until it has located a genuine detent, wait 60 seconds. Stop the vehicle engine, clear the DTC and retest

So you may want to look at the terrain response **** in the center console
General disclaimer: I may be wrong.

Jeff

 

Thanks for the insights! Updates:

- I discovered some furry friends have been taking up residence behind my battery and chewed through at least one wire. I spliced it and my brake light codes (P0504) went away, yet I still get the bong, "special programs unavailable", and no cruise control whenever the vehicle is at rest.

- I double checked the orientation of the brake light switch and it's correct.

- I do have the OEM trailer wiring harness that plugs in behind the left tail light. What should I check here? On that note, I occasionally use a brake controller which I plug in under the dash on the driver's side. I recently removed this and so the factory wiring is disconnected and dangling. I'll see what happens when I plug it back in.

- I think I've ruled out the clock spring as I swapped in a heated steering wheel (LR4) using BBS boards which required a different (heated) clock spring.

- When I use my terrain response ****, the messaging on the dash doesn't match the selection at the **** and it takes several seconds for the terrain response logo to appear on the dash. It's almost as if it's a full detent off, but I don't see how I can change the indexing. I suspect the remaining symptoms may be tied to the the terrain response circuit in some way such as:

chewed wire!

original PCB with a bit of corrosion on the rotary encoder

 

So you're not getting any of the error codes anymore, is that right?
Have you tried cleaning both your old and new terrain response boards with electrical contact cleaner and testing both?