P0402 - Exhaust Gas Recirculation (EGR) A Flow Excessive Detected
System
Powertrain (Engine & Gearbox)
Technical Description
The control module has detected a fault in the Exhaust Gas Recirculation (EGR) A Flow Excessive Detected (P0402).
Multimeter Test Points & Nominal Values
| Test Point / Component | Measurement | Nominal Target Range | Test Condition |
|---|---|---|---|
| Exhaust Gas Recirculation (EGR) A Flow Excessive Detected – Coil Resistance | Resistance (Ω) | 3 - 30 Ω (typical) | Connector disconnected at 20°C |
| Exhaust Gas Recirculation (EGR) A Flow Excessive Detected – Duty Cycle | PWM (%) | 5 - 95 % (modulates with target) | Engine running, actuator in control |
| Exhaust Gas Recirculation (EGR) A Flow Excessive Detected – Supply Voltage | Voltage (V) | 11.8 - 14.4 V | Ignition ON at connector |
Connector disconnected at 20°C
Engine running, actuator in control
Ignition ON at connector
Oscilloscope Waveform Analysis
2 ms/div, 20 V/divPossible Causes
Channel A:Verify dedicated wiring pins and signal pair for circuit A against the schematic.
Chafed or pinched wiring harness along the signal path to Exhaust Gas Recirculation (EGR) A Flow Excessive Detected
Internal mechanical wear or carbon deposits inside Exhaust Gas Recirculation (EGR) A Flow Excessive Detected
Defective internal output driver or reference circuit in the control module for Exhaust Gas Recirculation (EGR) A Flow Excessive Detected
Symptoms
4
Recommended Solution
Compare signal voltage and resistance between circuit A and companion circuit B at module connector.
Check for leaking seals, stuck-open metering valves, or out-of-calibration flow sensors.
Verify loaded supply voltage and harness terminal pins at Exhaust Gas Recirculation (EGR) A Flow Excessive Detected.
Check circuit continuity and ground-side voltage drop (< 0.05 V) for Exhaust Gas Recirculation (EGR) A Flow Excessive Detected.
Check supply and the low-side driver at the ECM connector. Replace the actuator or repair the circuit based on the readings.
Mechanic's Tip
Use the scan-tool output test with the scope on the control side at the same time. If duty changes but the actuator does not move, the valve is stuck — not the electrical fault you were chasing.