P0490 - Exhaust Gas Recirculation 'A' Control Circuit High
Last updated:
System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0490 is set when the Engine Control Unit (ECU) detects an abnormally high voltage signal in the Exhaust Gas Recirculation (EGR) control circuit. The EGR system recirculates a portion of exhaust gases back into the combustion chambers to lower peak combustion temperatures, reducing Nitrogen Oxide (NOx) emissions. A 'Circuit High' condition typically indicates that the ECU sees a voltage close to battery voltage on the control line when it should be grounded or modulated. This is often caused by a short to voltage in the wiring harness or an internal failure of the EGR valve solenoid. The ECU may respond by entering a 'Limp home' mode and disabling EGR functionality.
Possible Causes
Short circuit to B+ (battery voltage) in the EGR valve wiring harness
Failed EGR valve solenoid (internal electrical short)
Faulty EGR position sensor sending incorrect feedback signals
Poor engine ground connections or an internal ECU hardware fault
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
Do you also have
other fault codes?
See how P0490 connects with your other fault codes. Our advanced analysis tool identifies causal relationships and root causes directly.