C159C: Trailer brake control switch fault (Chevrolet, GMC)
C159C trailer brake control switch, Service Trailer Brake message
Severity: Inspect soon
The Service Trailer Brake message means the electric trailer brakes may not work on that drive. Your truck brakes still work, but towing without trailer brakes lengthens stopping distance.
It gets more serious if:
- Stop: Do not tow if the trailer brakes are disabled and the trailer is heavy; stop in a safe place if the red brake warning light is on or the pedal feels different. Toyota's owner's manual, used as a general benchmark, treats a red brake light as a stop condition.
C159C in short
On the 2022-2023 Chevrolet and GMC full-size trucks GM covers, C159C points to the trailer brake control switch. A Service Trailer Brake message appears when a trailer is connected, and the electric trailer brakes may not work on that drive. Have it checked before towing a loaded trailer.
These trucks have a built-in trailer brake controller that sends braking signals to a trailer with electric brakes. If the controller's switch reports a fault, the truck shows a Service Trailer Brake message and sets C159C.
GM's preliminary bulletin for 2022-2023 Silverado, Sierra, Tahoe, Suburban, Yukon XL and Escalade ESV says the message can appear when a trailer is connected and C159C symptom 49 may be set. Owner complaints say dealers pointed them to this bulletin and had no fix at the time.
The meaning here is limited to Chevrolet and GMC trucks covered by that bulletin. Other makes use the same code number differently and are not described.
Pick your make
C159C is a manufacturer-specific code: its meaning depends on who built the car.
Other makes: meaning not verified. Check with a scan tool that reads manufacturer definitions.
Most likely causes
Cause 1: Trailer brake control switch fault
Supported by vehicle data- Why it ranks here
- GM's bulletin names the trailer brake control switch for C159C on these trucks, and the NHTSA summary was read but not the full bulletin, so the label is based on the summary only.
- What would change this
- Rises if the dealer finds your VIN in the bulletin and the switch is flagged on a scan tool. Falls if the trailer wiring or plug is damaged instead.
Cause 2: Trailer plug or wiring problem
Possible — needs testing- Why it ranks here
- One complaint says the dealer tested the trailer brakes and found them working, so the trailer side is less likely, but it has not been ruled out in general.
- What would change this
- Rises if the message appears only with one trailer. Falls if it appears with several trailers.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Ask a GM dealer whether your VIN is covered by PIT5948 or a related trailer brake control program, and have them read the trailer brake controller data.
Warning:Trailer brakes affect stopping distance with a load. Do not tow with the message showing until it is checked.
IfThe dealer finds C159C with the trailer brake switch flagged
It meansThe switch is the likely cause.
IfThe fault appears only with one trailer
It meansCheck that trailer's plug and wiring.
Symptoms
- Service Trailer Brake message when a trailer is connected
- Trailer brakes disabled message after driving off
- Red brake warning light or soft pedal Gets more serious: stop and have it checked.
How to fix
This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.
On your vehicle
ChevroletYour car
2022–2023 · Silverado 1500
Supported by vehicle dataGM's bulletin and several owner complaints tie the Service Trailer Brake message to C159C on 2022-2023 Silverado 1500.
PIT5948BStatus unverified
Service Trailer Brake message with DTC C159C
2022–2023silverado-1500, suburban, tahoe · issued · NHTSA 10232813
Preliminary information: a Service Trailer Brake message shows with a trailer connected and C159C symptom 49 may be set for the trailer brake control switch. The NHTSA summary says GM engineering was working on it.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
GMCYour car
2022–2023 · Sierra 1500
Supported by vehicle dataThe same GM bulletin covers the Sierra 1500, and a 2022 owner complaint reports trailer brakes disabled with C159C.
PIT5948B-GMCStatus unverified
Service Trailer Brake message with DTC C159C
2022–2023sierra-1500, yukon-xl · issued · NHTSA 10232813
Preliminary information: a Service Trailer Brake message shows with a trailer connected and C159C symptom 49 may be set for the trailer brake control switch. The NHTSA summary says GM engineering was working on it.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
No curated relationships for C159C yet.
Sources and review
- GM preliminary information PIT5948B: Service Trailer Brake message with DTC C159C
- NHTSA complaint ODI 11497601 (2022 Silverado 1500, C159C)
- Toyota Camry Owner's Manual (OM06291U)
- NHTSA complaint ODI 11490095 (2022 Sierra 1500, C159C)
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error