What it means
The exhaust brake activation input - typically from a stalk lever, brake pedal switch, or vehicle bus message - shows a circuit fault. The ECU cannot accept a request to engage the exhaust brake, which limits engine braking on heavy vehicles.
At a glance
- Usually lights the check-engine light
How it works
The exhaust brake input circuit carries the driver’s request—through a switch, pedal input, or vehicle network—to the control module. This code sets when the module detects an electrical fault in that request circuit and may be unable to accept an engage command.
Common causes
Most likely first.
- Faulty exhaust-brake switch or input sensor
- Open or short in input wiring
- Loose or corroded connector
Symptoms
- Exhaust brake may not engage when requested
- Exhaust-braking response may be unavailable or inconsistent
How to diagnose it
- Check freeze-frame data and scan-tool input status to see whether the exhaust-brake request is detected when the driver operates the control.
- Inspect the exhaust-brake switch or input sensor and its connector for looseness, corrosion, damage, or misadjustment.
- Follow the input wiring to the module, looking for open, shorted, pinched, or chafed sections and poor connections.
- Use the wiring diagram to test the input circuit for continuity and shorts, and check the switch or sensor output while operated.
- If the request arrives over the vehicle bus, check for related communication or input faults and confirm the reported request with the manufacturer’s diagnostic information.
Common fixes
- Reconnect or secure a loose exhaust-brake input connector.
- Repair an open, short, or chafed section of input wiring.
- Adjust or replace a faulty exhaust-brake switch or input sensor.
- Repair corroded terminals or a damaged connector.
Can I keep driving?
The truck may still move normally, but exhaust braking may be unavailable, increasing reliance on the service brakes on descents. Use a lower gear and avoid steep or long downhill routes until the input fault is fixed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.