P0490 OBD-II Trouble Code: Exhaust Gas Recirculation "A" Control Circuit High

P0490 code definition

If the powertrain control module, or PCM, has detected an abnormally high rate of

voltage flow within the exhaust gas recirculation system, or EGR, it will store the P0490

code. It is commonly associated with the P0489 code, which indicates that the voltage

within the same system is abnormally low.

What the P0490 code means

The EGR works to prevent NOx from forming in the cylinders of a vehicle. This is

achieved by a computer system that opens and closes the EGR in order to maintain

cylinder head temperature. If this computer fails to register a voltage change in the

EGR, it will believe that the EGR is not opening or closing, and will cause the P0490

code to be stored in the PCM.

What causes the P0490 code?

Most commonly, a clogged EGR or DPFE passage are to blame for the P0490 code.

There may also be a short to the battery voltage, or a failed ECU causing this code.

Other causes may include:

• Faulty EGR sensor

• Faulty EGR valve

• Faulty EGR solenoid

• Faulty MAP sensor

• Broken vacuum line

• Faulty connectors or electrical wiring

What are the symptoms of the P0490 code?

In most cases, the P0490 code is not preceded by any symptoms. The vehicle owner

will be alerted to a problem by the illumination of the Check Engine Light. However,

some vehicles may run roughly, or may be difficult to start. Vehicle owners may

experience a decrease in power, or a decrease in fuel economy.

How does a mechanic diagnose the P0490 code?

In order to diagnose the P0490 code, a technician needs to check the PCM memory

with an OBD-II scanner. When the P0490 code is returned, they should inspect the

electrical wiring and connectors, to be sure that the issue isn’t being caused by a simple

short or disconnected wire. When any issues in the wiring have been addressed, they

should clear the code and retest the system. If the code is still being stored, they will

then consider other repair options to address the P0490 code.

Common mistakes when diagnosing the P0490 code

The most common mistake when diagnosing the cause of the P0490 code is to

automatically replace the EGR valve. This part is not faulty as often as many other

components of the EGR system.

How serious is the P0490 code?

Because the buildup of NOx in a vehicle’s cylinders can be very harmful, the presence

of the P0490 code is very serious. A properly operating EGR is also a key component

for getting good fuel economy. This repair should be addressed immediately.

What repairs can fix the P0490 code?

After ensuring that the electrical components are not responsible for the storage of the

P0490 code, the mechanic has several repair options available:

• Use a scanner to monitor EGR function, and manually compare the information to the

manufacturer’s specifications.

• Check and repair the EGR valve, control solenoid, sensor, or DPFE sensor, as

necessary.

• Disconnect the vacuum line, and manually apply vacuum to the EGR valve to observe

the operation.

• Remove the EGR valve and clear any clogs.

• Check that the computer is working correctly, and replace if necessary.

• Test all connectors and wiring for the PCM, and repair or replace as necessary.

After each of these repairs, the code should be cleared and the system should be

retested. The more repairs that are checked off the list, the easier it will be for a

technician to narrow down the true cause behind the P0490 code.

Additional comments for consideration regarding the P0490 code

If the P0490 code is detected in a vehicle that has fewer than 100,000 miles, check the

manufacturer’s warranty or dealership’s warranty. The EGR system is typically covered

under standard warranties, and the cost of replacement or repair may be covered by the

warranty.

Need help with a P0490 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to

diagnose and repair your vehicle. Get a quote and book an appointment

online or speak to a service advisor at 1-800- 701-6230.