1

2021 M2 BHM/CHM issue?

Ericka Natali 34 posts since May 14, 2015

2021 M2 BHM/CHM issue? Sep 8, 2020 12:56 PMGood Morning All!

2021 M2 Vin ME6099 -

Customer complaint - Left tail light goes out when brake lights come on.

Lots of previously active BHM codes

524247/7 BHM/CHM Ignition Mismatch 126 Ct

879/6 Left Turn Lamp Circuit 67 Ct

Wiring inspection - no damage. Wire testing shows power is good at all points

Anyone else run into this? Could the issue be internal to the CHM?

Landover Laptops 1 posts since Feb 21, 2019

Re: 2021 M2 BHM/CHM issue? Sep 8, 2020 3:00 PM

Sounds like a bad ground, or possibly a bulb not install correctly

Kyle Siebert 3,908 posts since Nov 14, 2014

Re: 2021 M2 BHM/CHM issue? Sep 8, 2020 3:19 PM

On the left rear, are there two red lamp assembly’s?  Both work for marker lamps I take it?  Butonly one works for the brake lamp?

It sounds like it may be miswired at the body builder connecton. You could back probe at the CHM for both

rear marker lamp circuits to see if they both are on with brake lamps on.

Robert Cadell Jr 2,590 posts since Nov 9, 2014

Re: 2021 M2 BHM/CHM issue? Sep 8, 2020 10:14 PM

does this unit pull a trailer? how was the unit built, meaning single rear tail lights and customer added the

option for dual lights? Had a similar unit it pulled a trailer and needed a parameter change for that option.

Just some thoughts.

Robert Cadell Jr 2,590 posts since Nov 9, 2014

Re: 2021 M2 BHM/CHM issue? Sep 8, 2020 10:17 PM

879 6 Front left turnlamp — current

The BHM mea-sures the cur-rent on this cir-

38L CHM C3, N

2021 M2 BHM/CHM issue?

2

above expectedvalue

cuit when thelamp is com-manded ON.This fault indi-cates that thelamps connec-ted to this circuitare drawing mo-re current thanthe circuit is de-signed to sup-ply, or there is awiring fault shor-ting this circuitto ground. fromthe m2 manual 54.12.410 Bulk-head ModuleFault Code In-formation

Michael Palumbo 1,371 posts since Nov 13, 2014

Re: 2021 M2 BHM/CHM issue? Sep 9, 2020 11:05 AM

If it is the factory Grote light box from BOM 294, it could be as simple as the 1157 bulb. I have seen 1156

bulbs in the 1157 socket behave like this.

Talbert Simonian 1,741 posts since Nov 21, 2014

Re: 2021 M2 BHM/CHM issue? Sep 11, 2020 12:17 AM

Yes it could be a issue with the CHM. I think Robert Cadell Jr is leading the correct direction. I would unplug

the harness and load test it. Then check it to Ground.

Robert Cadell Jr 2,590 posts since Nov 9, 2014

Re: 2021 M2 BHM/CHM issue? Sep 11, 2020 12:21 AM

And to add on Talbert Simonian comment cross ohm the circuits its a me thing make sure they arent shorted

together.

Kyle Siebert 3,908 posts since Nov 14, 2014

Re: 2021 M2 BHM/CHM issue? Sep 11, 2020 1:58 AM

If it was a parameter issue, it would be both sides acting up though.

Jon Cecil 783 posts since Nov 25, 2014

Re: 2021 M2 BHM/CHM issue? Sep 11, 2020 3:39 AM

2021 M2 BHM/CHM issue?

3

Looking through schematics makes it seem it is a body builder issue. Power for the left tail light isshared with the right tail light. Like Kyle Siebert said with a parameter, any issue with circuit 23should be affecting both tail lights. Power leaves BHM C1-K to CHM C3-P. Power then continuesout of CHM C2-G, C1-D, C1-E, and C1-F. There shouldn’t be any wires populated in C1-E or C1-F. C2-G goes to the trailer tail relay in the trailer PDM. If only one tail light is having an issue, Itreally seems to be a body builder issue. I wouldn’t be surprised if the issue lies in the 7-way. 

Ericka Natali 34 posts since May 14, 2015

Re: 2021 M2 BHM/CHM issue? Sep 11, 2020 12:25 PM

* Update *

Cleared codes and customer took truck for body inspection.

Checked codes on return - 12 previously active BHM codes. Left turn lamp is working.

1-4 counts for missing smart switch, ignition switch, vehicle speed, wiper park mismatch, data error, cab dome

light, cigar lighter, starter relay, wiper motor speed & back-up light and alarm horn.

27 Ct - 524247/7 BHM/CHM Ignition Mismatch

3 Ct - 879/6 Left Turn Lamp Circuit

Road tested, hit a bump, light out. On the driver side found chassis harness pinched on top of hose shield

12-22261-000 under the cab causing short. Opened up and found 4 bare wires. Road tested, light works, no

codes came back.

Thank you all for your feedback!

Robert Cadell Jr 2,590 posts since Nov 9, 2014

Re: 2021 M2 BHM/CHM issue? Sep 11, 2020 12:32 PM

Great Job, Good Hunting my friend

Rob “Doc” CadellDTNA Master Tech/Elgin Lead Technician

Trans Chicago Freightliner BFWD

Shorewood,IL

(803)-917-5397