Tail Error Message - Long Post
11-21-2012, 07:12 PM
#1
Rennlist Member
Thread Starter
Tail Light Error Message - Long Post
Thought I'd share a recent experience trying to track down an elusive "tail light" error message.
Symptom:
Whenever stopped at a traffic light or other full stop situations, with foot firmly on the brake, a "tail light" error message (not "stop lamp") appears in the instrument cluster, along with the central warning light. Happens in broad daylight with no running lights on, and only when you come to a dead stop with foot on the pedal for 2-3 seconds, then the error light appears. Does not happen under normal braking while the car is moving on the highway, only at a dead stop with foot on the pedal. Error message and central warning light go out immediately when you remove your foot from the brake pedal.
All exterior running lights (including the tail and side lights) work as designed (no burned out bulbs) and no fuse issues.
Background:
Car in full hibernation for the past two years and normally driven only in summers previous to that.
Recent work:
Changed all fluids, replaced timing belt & water pump, tensioner rebuilt, repaired ABS wire harness on one wheel, rebuilt alternator, new heater valve & short hose, cleaned all grounds and replaced battery ground strap, replaced all fuel hoses with Greg Brown's premium space age fuel hoses, replaced "Toothed-Belt" error light in pod and replaced odometer gear.
First thought:
Maybe the problem was created while replacing the odometer gear or the belt warning light in the pod. Resisted that impulse and decided to trust the bulb warning system. Not very good with a multi-meter, so decided to remove each tail light assembly and to thoroughly clean each bulb socket and the bases of all bulbs in the assembly. Did that. Tail light wire harnesses and plugs looked good also.
Retest:
No joy. Still had problem (only when stopped fully with foot firmly on the brake). Goes away when you release the brake pedal. All lights work.
Decided to replace all of the tail light bulbs with new bulbs since I had several spares from Roger. Did that and retested. Problem still existed.
Considered that it might be the BCU itself, but decided to step back and think about it a little more. Reasoned that there must be something related to increased resistance tripping the BCU only when the brakes were fully applied for more than a second or two.
Since I had to check the lights by myself, I used a boat brush with telescoping handle (between the brake pedal and front seat back) to keep the brakes activated (engine off) with all lights on while I was at the rear of the car.
As before, all tail lights appeared to work properly, but after a minute or two, I noticed a very slight difference in the brightness of the drivers-side tail light assembly vs. the passengers-side tail light assembly. The left side was slightly dimmer.
Removed the left tail light assembly, pulled apart the harness plugs and cleaned all the pins and pin sockets with a small points file, then sprayed with CRC, and dried thoroughly. When I started to put the plugs back together, I noticed that one of the pin sockets on the tail light harness plug was pushed into the rubber plug further than the rest. Took a little doing but I was able to pull it out slightly so that it was almost even with the others.
Reconnected the plugs & retested. No longer a difference in brightness under sustained brake pressure and no further tail light error messages in the cluster.
Conclusion:
The "tail light" error may have been caused by the recessed pin socket not making full contact, but it is more likely that all of the pins and pin sockets needed a thorough cleaning to make better contact.
Lessons learned:
Although I wanted to jump to early conclusions about the possible causes, it was better to trust the system as it was designed. Also, it would have been easier to find the problem if I had used a meter at the beginning.
Just wanted to share this in case it helps someone else.
Symptom:
Whenever stopped at a traffic light or other full stop situations, with foot firmly on the brake, a "tail light" error message (not "stop lamp") appears in the instrument cluster, along with the central warning light. Happens in broad daylight with no running lights on, and only when you come to a dead stop with foot on the pedal for 2-3 seconds, then the error light appears. Does not happen under normal braking while the car is moving on the highway, only at a dead stop with foot on the pedal. Error message and central warning light go out immediately when you remove your foot from the brake pedal.
All exterior running lights (including the tail and side lights) work as designed (no burned out bulbs) and no fuse issues.
Background:
Car in full hibernation for the past two years and normally driven only in summers previous to that.
Recent work:
Changed all fluids, replaced timing belt & water pump, tensioner rebuilt, repaired ABS wire harness on one wheel, rebuilt alternator, new heater valve & short hose, cleaned all grounds and replaced battery ground strap, replaced all fuel hoses with Greg Brown's premium space age fuel hoses, replaced "Toothed-Belt" error light in pod and replaced odometer gear.
First thought:
Maybe the problem was created while replacing the odometer gear or the belt warning light in the pod. Resisted that impulse and decided to trust the bulb warning system. Not very good with a multi-meter, so decided to remove each tail light assembly and to thoroughly clean each bulb socket and the bases of all bulbs in the assembly. Did that. Tail light wire harnesses and plugs looked good also.
Retest:
No joy. Still had problem (only when stopped fully with foot firmly on the brake). Goes away when you release the brake pedal. All lights work.
Decided to replace all of the tail light bulbs with new bulbs since I had several spares from Roger. Did that and retested. Problem still existed.
Considered that it might be the BCU itself, but decided to step back and think about it a little more. Reasoned that there must be something related to increased resistance tripping the BCU only when the brakes were fully applied for more than a second or two.
Since I had to check the lights by myself, I used a boat brush with telescoping handle (between the brake pedal and front seat back) to keep the brakes activated (engine off) with all lights on while I was at the rear of the car.
As before, all tail lights appeared to work properly, but after a minute or two, I noticed a very slight difference in the brightness of the drivers-side tail light assembly vs. the passengers-side tail light assembly. The left side was slightly dimmer.
Removed the left tail light assembly, pulled apart the harness plugs and cleaned all the pins and pin sockets with a small points file, then sprayed with CRC, and dried thoroughly. When I started to put the plugs back together, I noticed that one of the pin sockets on the tail light harness plug was pushed into the rubber plug further than the rest. Took a little doing but I was able to pull it out slightly so that it was almost even with the others.
Reconnected the plugs & retested. No longer a difference in brightness under sustained brake pressure and no further tail light error messages in the cluster.
Conclusion:
The "tail light" error may have been caused by the recessed pin socket not making full contact, but it is more likely that all of the pins and pin sockets needed a thorough cleaning to make better contact.
Lessons learned:
Although I wanted to jump to early conclusions about the possible causes, it was better to trust the system as it was designed. Also, it would have been easier to find the problem if I had used a meter at the beginning.
Just wanted to share this in case it helps someone else.
Last edited by mdkelly1; 12-05-2012 at 04:11 PM.
11-21-2012, 07:30 PM
#2
Good write up David, I'm sure it will come in very useful.
11-21-2012, 10:49 PM
#3
Rennlist Member
Nice job. I am going to try this out- developed a recent intermittent STOP lamp warning and I see no visible bulb issues. Going to clean the harness up, can't hurt. Thanks.
03-30-2015, 06:02 PM
#4
Rennlist Member
I did fix the issue- I removed both light assemblies and the harnesses from the assemblies. Cleaned everything very thoroughly (Deoxit, etc), found a small bit of corrosion, and some electrical tabs a little out of whack. Put it all back together and have been issue-free for over 6 months.
03-30-2015, 06:58 PM
#5
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
I think it was a build up of resistance at the shared ground connection for the whole cluster. Likely it only fails at a stop because the voltage droops a little at idle affecting the measurement accuracy...
There are voltage comparators watching the voltage drop across series resistances in the bulb supplies and comparing the differences side to side. Both difference & magnitude faults are flagged - probably a difference fault here if you could see a brightness change side to side with brakes on. Voltage is detected wrt ground on the marker light too in this case because the local ground at the light cluster is rising due to the brake lights. The other side of the marker filaments (that is usually driven by the light switch) will also rise for that side and will be different to to the other side causing a differential fault.
Alan
There are voltage comparators watching the voltage drop across series resistances in the bulb supplies and comparing the differences side to side. Both difference & magnitude faults are flagged - probably a difference fault here if you could see a brightness change side to side with brakes on. Voltage is detected wrt ground on the marker light too in this case because the local ground at the light cluster is rising due to the brake lights. The other side of the marker filaments (that is usually driven by the light switch) will also rise for that side and will be different to to the other side causing a differential fault.
Alan
