Code
P0490
Generic
P — Powertrain
EGR A Control Circuit High
Views:
UK: 18
EN: 30
RU: 38
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the EGR control circuit
- Corroded, damaged, or disconnected connector or wiring
- Faulty EGR solenoid/actuator or valve
- Poor or missing ground at the EGR circuit
- Faulty ECM or driver transistor
- Incorrect repairs or aftermarket modifications affecting wiring
Symptoms
- Check Engine light (MIL) illuminated
- Reduced engine performance or hesitation
- Rough idle or increased idle variation
- Poor fuel economy
- Failed emissions test or increased exhaust emissions
- Possible limp-home mode on some vehicles
What to check
- Read and record freeze frame and live data with a scan tool; confirm P0490 and note related codes
- Perform a visual inspection of EGR harness and connector for damage, corrosion, or water
- Backprobe the EGR control connector and measure voltage and/or duty cycle while commanding the EGR ON/OFF with a scan tool
- Measure coil resistance of the EGR solenoid/actuator (compare to manufacturer spec)
- Check continuity between ECM pin and EGR connector pin; check for short to battery or open circuit
- Wiggle test wiring while monitoring signal to see if fault is intermittent
Signal parameters
- With key ON engine OFF: control circuit may show battery voltage or reference voltage depending on vehicle design; consult vehicle wiring diagram
- When commanded OFF: output should be at the expected inactive level (low or high depending on driver type); a sustained higher-than-expected voltage indicates fault
- When commanded ON: circuit should show a change (switch to ground, switch to supply, or PWM duty change) consistent with OEM expected behavior
- Typical EGR solenoid coil resistance is often in the tens of ohms (commonly 10–60 Ω) — check the specific service data for the vehicle
- Use oscilloscope to confirm expected PWM duty cycle or switched waveform when the ECM commands the valve
Diagnostic algorithm
- Connect a scan tool, confirm P0490 and note any additional EGR or related codes. Record freeze-frame/live data.
- Visually inspect EGR valve/solenoid, connector, and harness for damage, corrosion, loose pins, or heat damage.
- With battery voltage present, backprobe the connector. With key ON engine OFF, observe connector voltage. Compare to expected for that design (reference OEM data).
- Command the EGR ON/OFF from the scan tool. Observe the control signal change. If the signal is higher than expected when commanded, suspect short to voltage or driver fault.
- Remove connector and measure coil resistance of the EGR solenoid. If out of spec or open/shorted, replace the solenoid/valve.
- Check continuity between the EGR connector signal pin and the ECM pin. Check for short to battery (voltage present on harness when disconnected) and for short to ground.
- Verify good ground(s) for the EGR circuit. Repair any poor ground connections.
- If wiring and component test normal, consider ECM output driver failure. Before ECM replacement, confirm with wiring pin-to-pin tests and, if possible, substitute known-good ECM or perform bench/technical procedures per manufacturer.
- Repair or replace faulty wiring, connector, or EGR valve/solenoid. Clear codes and perform road/functional test to confirm repair and that the DTC does not return.
Likely causes
- Pinched or chafed harness contacting a power source (short to 12V)
- Water intrusion or corrosion in the EGR connector causing high voltage reading
- Stuck/open EGR control valve with internal shorted coil
- Loose or broken ground at the valve or engine block
- ECM output stage failed and driving high
Fault status
Status
EGR A control circuit voltage higher than expected; ECM detected abnormal high signal on EGR A control circuit and set DTC P0490.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
P0490
LAND ROVER
P — Powertrain
Exhaust Gas Recirculation Control - High Circuit
Views:
UK: 10
EN: 19
RU: 24
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the EGR control circuit
- Corroded, damaged, or disconnected connector or wiring
- Faulty EGR solenoid/actuator or valve
- Poor or missing ground at the EGR circuit
- Faulty ECM or driver transistor
- Incorrect repairs or aftermarket modifications affecting wiring
Symptoms
- Check Engine light (MIL) illuminated
- Reduced engine performance or hesitation
- Rough idle or increased idle variation
- Poor fuel economy
- Failed emissions test or increased exhaust emissions
- Possible limp-home mode on some vehicles
What to check
- Read and record freeze frame and live data with a scan tool; confirm P0490 and note related codes
- Perform a visual inspection of EGR harness and connector for damage, corrosion, or water
- Backprobe the EGR control connector and measure voltage and/or duty cycle while commanding the EGR ON/OFF with a scan tool
- Measure coil resistance of the EGR solenoid/actuator (compare to manufacturer spec)
- Check continuity between ECM pin and EGR connector pin; check for short to battery or open circuit
- Wiggle test wiring while monitoring signal to see if fault is intermittent
Signal parameters
- With key ON engine OFF: control circuit may show battery voltage or reference voltage depending on vehicle design; consult vehicle wiring diagram
- When commanded OFF: output should be at the expected inactive level (low or high depending on driver type); a sustained higher-than-expected voltage indicates fault
- When commanded ON: circuit should show a change (switch to ground, switch to supply, or PWM duty change) consistent with OEM expected behavior
- Typical EGR solenoid coil resistance is often in the tens of ohms (commonly 10–60 Ω) — check the specific service data for the vehicle
- Use oscilloscope to confirm expected PWM duty cycle or switched waveform when the ECM commands the valve
Diagnostic algorithm
- Connect a scan tool, confirm P0490 and note any additional EGR or related codes. Record freeze-frame/live data.
- Visually inspect EGR valve/solenoid, connector, and harness for damage, corrosion, loose pins, or heat damage.
- With battery voltage present, backprobe the connector. With key ON engine OFF, observe connector voltage. Compare to expected for that design (reference OEM data).
- Command the EGR ON/OFF from the scan tool. Observe the control signal change. If the signal is higher than expected when commanded, suspect short to voltage or driver fault.
- Remove connector and measure coil resistance of the EGR solenoid. If out of spec or open/shorted, replace the solenoid/valve.
- Check continuity between the EGR connector signal pin and the ECM pin. Check for short to battery (voltage present on harness when disconnected) and for short to ground.
- Verify good ground(s) for the EGR circuit. Repair any poor ground connections.
- If wiring and component test normal, consider ECM output driver failure. Before ECM replacement, confirm with wiring pin-to-pin tests and, if possible, substitute known-good ECM or perform bench/technical procedures per manufacturer.
- Repair or replace faulty wiring, connector, or EGR valve/solenoid. Clear codes and perform road/functional test to confirm repair and that the DTC does not return.
Likely causes
- Pinched or chafed harness contacting a power source (short to 12V)
- Water intrusion or corrosion in the EGR connector causing high voltage reading
- Stuck/open EGR control valve with internal shorted coil
- Loose or broken ground at the valve or engine block
- ECM output stage failed and driving high
Fault status
Status
EGR A control circuit voltage higher than expected; ECM detected abnormal high signal on EGR A control circuit and set DTC P0490.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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