NOTE: Repair any engine knocking sounds before performing test.

Turn ignition off. Remove BACK-UP fuse (7.5-amp) from underhood fuse/relay box for 10 seconds to reset ECM. Warm engine until cooling fan comes on. Set engine speed at 3000-4000 RPM for 10 seconds. Check ECM for fault codes. If Code 23 is not present, problem is intermittent. Check for poor connections at ECM, knock sensor and wiring harness connectors.
Test drive vehicle and retest. If Code 23 is present, turn ignition off. Connect ECM Test Harness (07LAJ-PT3010A) to ECM connectors, leaving ECM disconnected. See Figure. Disconnect knock sensor connector. Check for continuity between test terminal D3 and body ground. If continuity is present, repair short in Red/Blue wire between ECM terminal D3 and knock sensor.
If continuity is not present, check for continuity between test terminal D3 and knock sensor connector Red/Blue wire terminal. If continuity is not present, repair open in Red/Blue wire between ECM connector terminal D3 and knock sensor.
If continuity is present, reconnect knock sensor. Replace knock sensor with a known good unit. Warm engine to normal operating temperature. Set engine speed at 3000-4000 RPM for 10 seconds. Check ECM for fault codes. If Code 23 is not present, replace original knock sensor. If Code 23 is present, replace ECM and retest.

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.

Safety Warning

Code 23: Knock Sensor (1.8L GS-R)