P0402 - EGR Flow Excessive Detected

The Camshaft Position (CMP) sensor circuit is monitored by the Powertrain Control Module (PCM). The test for excessive EGR flow fails when the PCM detects an increasing engine roughness at off idle engine speed based on the signal received from the CMP sensor. If the engine roughness decreases when the Exhaust Gas Recirculation (EGR) control solenoid valve is commanded closed, it is determined that the EGR modulator valve is not operating properly.

Possible Causes:
- EGR modulator valve
- EGR valve
- CMP sensor
- EGR control solenoid valve
- Loose or disconnected rubber tube
- Blocked exhaust valve
- Orifice
- Mass Air Flow (MAF) sensor

Diagnostic Aids:
Monitor and record RPM PID at off idle speed, there should not be any sudden changes in the RPM PID readings or engine roughness. If there are sudden changes in the RPM PID readings and the engine is running rough command EGR valve off. If off idle roughness stops the EGR modulator valve is at fault.