VZ Commodore DTS C0161 Stop Lights Circuit Crazy Problem

[Dutch]

I have a VZ Commodore that suddenly threw an ABS, ESC and Cruise Control fault. The Cruise Control will not engage and the ABS warning and ESC warning on LCD dashboard. I put the TECH2 on the beasty and the only fault code showing was C0161 "Stop Light Control Circuit Problem". The weird thing is that the stop lights work fine. The fuses are fine and the globes all work.

I thought that it might be one of the 2 x foot brake switches under the dashboard (because there are two switches on the foot brake) so I went to the wreckers and after a lot of stuffing around got two replacement switches. I then retested for trouble codes and was disappointed with it throwing the same warming ABS Fault and Electronic Stability Control Warning on the LCD dash. C-0161 still showing up.

Even though it was saying "stop light circuit fault" I thought that it might be the Bosch ABS electronic module that bit the dust. So after another trip down to the wreckers and I came back with a replacement $100 ABS module (one with Electronic Stability Control) with the matching Bosch part number. After testing the replacement ABS module...... yep! Bloody C-0161 code persisted.

I'm kind of at my wits end with this problem. Any ideas as to what else I can try?

 

[99notout]

C-0161 is just the brake switch circuit fault, here is part of the fault code check list for C-0161. The ABS is still meant to work with this code present, hope it's just a crap connection or the switch out of parameter. Good luck.

 

[Dutch]

Thanks for the attachment. I have something similar from Bosch.

Problem fixed this morning - I found this Bosch pdf which explains that the ECM is measuring the battery voltage drop to determine the
state of the brake lights and not the pedal switch itself. How weird is that? It would explain why a stuffed battery starts DTS codes if the voltage
starts dropping.

I took out the light globes when testing the circuit and was surprised to see that they are LED globes like in the photo above. After reading the Bosch explanation, it started me thinking that if the globes are LED, then perhaps they aren't pulling enough current for the ECM to detect the brake lights operating. (But the LED's have obviously been in the vehicle since I bought it.) The current draw on the LED's is much lower than the normal filament globes. So I tried 2 x standard filament globes from another vehicle and YOU WOULDN'T BELIEVE IT!!!!! ARGH!!!!!! $%#@%$^&^& THE ABS, ESC AND CRUISE CONTROL NOW WORK FINE!!!! and the DTS fault code disappeared after it was cleared. Perhaps something has changed in the battery over time and suddenly it wasn't able to read the low LED current draw as a "tail lights on" situation.

NEW RULE - "DON'T USE LED BRAKE LIGHTS IN YOUR VZ"

 

[99notout]

Perfect result, glad you worked it out!