OBD-II Diagnostic Trouble Code
C0162 — Stop Lamp Switch B Failure
C0162 indicates a failure of the second stop lamp switch circuit (switch B). Many trucks use a dual-contact brake switch, one normally open and one normally closed, and the module expects them to change in opposite directions; C0162 sets when switch B does not agree with switch A. The exact code definition can differ by OEM.
Severity 2/5
Truck-relevant
Service soon
Severity
Service soon
Stop Lamp Switch B Failure
Code
C0162
Category
Chassis
Subsystem
Brakes
Truck-relevant
Yes
What this means for truckers
C0162 (Stop Lamp Switch B Failure) — secondary brake light switch failed. Same fix as C0090.
Before you replace parts — try this first
C0162 on the Brakes system is most often failed or misadjusted dual-contact brake switch — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
ABS, traction control or stability control lights on, cruise control may not work, and brake lights may act incorrectly. Base braking is unaffected. The engine ECM may also log a brake switch fault that blocks cruise or PTO operation.
Common causes
- CommonFailed or misadjusted dual-contact brake switch ($40–$200)
- OccasionalOpen or shorted wire for switch B ($80–$300)
- OccasionalBlown fuse feeding the switch circuit ($10–$80)
- RareModule input failure ($600–$2000)
How to fix
Watch both brake switch inputs on a scan tool while pressing the pedal
When to use: To see which contact is not changing
Adjust the switch so both contacts change at the correct pedal travel, or replace it
When to use: Switch is late, stuck or out of adjustment
Check fuse and wiring for the switch B circuit
When to use: Switch tests good off the truck
Clear codes and road test with several brake applications
When to use: After any repair to confirm the fix
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → C0110 — Pump Motor Circuit Malfunction
- → C0121 — Valve Relay Circuit Malfunction
- → C0131 — ABS Pressure Sensor Circuit
- → C0161 — ABS / TCS Brake Switch Circuit
- → C0186 — Yaw Rate Sensor Bias Circuit
Frequently Asked Questions
Can I drive with code C0162?
C0162 is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix C0162 on a commercial truck?
Total repair cost ranges $10–$2000 depending on the root cause. The cheapest fix is usually the first one listed below — Failed or misadjusted dual-contact brake switch — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will C0162 fail a DOT inspection?
C0162 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between C0162 and related codes?
C0162 is closely related to: C0110 (Pump Motor Circuit Malfunction), C0121 (Valve Relay Circuit Malfunction), C0131 (ABS Pressure Sensor Circuit), C0161 (ABS / TCS Brake Switch Circuit). These codes share the same subsystem (brakes) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only C0162 is set without the companions, the issue is more isolated.
How do I prevent C0162 from coming back after a repair?
For C0162 (Stop Lamp Switch B Failure), prevention centers on the brakes system. Clean wheel speed sensors at every brake service. Inspect tone rings for cracks or rust. Keep ABS sensor harnesses away from chafe points. Don't drive through deep water that can flood the rear wheel-speed sensor connectors.