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
- Check and repair the EGR valve, control solenoid, sensor, or DPFE sensor, as
- Disconnect the vacuum line, and manually apply vacuum to the EGR valve to observe
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
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