Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit/System Description
The engine control module (ECM) identifies engine misfire by detecting variations in crankshaft speed. Crankshaft speed variations can also occur when a vehicle is operated over a rough road. The antilock brake system (ABS) can detect if the vehicle is on a rough surface based on wheel acceleration/deceleration data supplied by each wheel speed sensor. This information is sent to the ECM by the electronic brake control module (EBCM) through pulse width modulation (PWM) serial data line. The ECM then uses this information to determine if the crankshaft variations are being caused by an actual engine misfire or from being driven on a rough surface.
If the ABS is found to be malfunctioning, the ECM will still continue to detect for misfire. However, if a misfire DTC is set, this additional DTC will also be set, indicating that rough surface data was not usable during the misfire detection due to the ABS malfunction.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.