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Error Code P0490 is defined as Exhaust Gas Recirculation (EGR) “A” Control Circuit High. This means the vehicle’s computer has detected an abnormally high voltage within the EGR, often caused by clogging.
This error code is generic, meaning it applies to all vehicle makes and models made since 1996 up to present or those equipped with the OBD-II system. Specifications on the definition, troubleshooting, and repairs of course, vary from one make and/or model to another.
This code refers to a problem with the EGR (Exhaust Gas Recirculation) system, specifically on its electrical aspect. The EGR works by preventing the formation of harmful NOx (Nitrogen Oxide) from forming in the cylinders and escaping to the atmosphere. It’s operated by the PCM (powertrain control module, also known as engine control module in other vehicle makes), which opens or closes the EGR as the temperature, load, and speed dictates to keep proper cylinder head temperature. A potentiometer is also included in the EGR solenoid to signal the position of the EGR pintle (the operating mechanism that opens and closes the passages).
Error Code P0490 happens when the PCM detects an abnormally high rate of voltage flow within the EGR system.
This code is also associated with P0489, which means the voltage within the same system is abnormally low.
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other symptoms include:
- Rough ridding
- Hard starting or no start condition at all
- Decrease in power
- Increase in fuel consumption
Common causes of this code include:
- Short to ground
- Short to battery voltage
- Defective EGR pintle
- Defective EGR solenoid
- Bad connector with pushed out pins
- Defective EGR
- Corrosion in connector or faulty wiring
- Bad PCM
How to Check
A common start for diagnosing this code is by the use of an OBD-II scanner to check for the stored code.
Next, technicians proceed on checking all the wiring, electrical connectors, and harnesses for damaged or defects.
Then they inspect the connectors, vacuum hoses, and lines for leaks or any signs of damage.
Next, they determine how the EGR valve is controlled by the PCM or vacuum.
They also monitor the EGR function and compare it with the recommendations set by the manufacturer.
Next, they determine whether the EGR valve is sticking or not. They will have to use a handheld vacuum pump to observe the EGR operation to determine if the valve opens.
If the vehicle doesn’t stall when the valve opens, they will have to check for clogged EGR passages.
If the engine stalls, then they will have to check the EGR control solenoid if it’s working.
Next, they will test the EGR control solenoid connector for a voltage and the ground signal.
Next, they will test the voltage signal between the PCM and the EGR electrical connector.
Lastly, technicians will check for signs of damage, burnt, or loose wiring at the EGR valve and control solenoid, or the EGR and the DPFE sensor.
How to Fix
Depending on the diagnosis, the common repairs for this code include:
- Repair or replacement of damage or loose connectors, harnesses, and wirings
- Repair or replacement of broken and leaking vacuum hoses and lines
- Repair or replacement of damaged or faulty EGR control solenoid
- Cleaning the EGR passages off of carbon
- Clearing the codes, test drive the vehicle and rescan to see if the codes reappear
- Replacement of damaged or defective EGR valve
EGR valve replacement is expensive, and in many cases, the problem is simply caused by a blown gasket or damaged wiring, which is why it’s important to conduct a thorough diagnosis.