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Technical Description of OBD-II Trouble Code
The control circuit for Exhaust Gas Recirculation “A” is experiencing high levels of activity.
What does that mean?
This code is a generic powertrain code that applies to all makes and models manufactured from 1996 onwards. However, the specific steps for troubleshooting will vary depending on the vehicle.
This engine trouble code indicates a failure in the electrical aspect of the EGR (exhaust gas recirculation) system. The EGR is a crucial component of the vehicle’s emission system, designed to prevent the formation of harmful Nox (oxides of nitrogen) in the cylinders.
The EGR is controlled by the engine management computer, which opens or closes it based on factors such as load, speed, and temperature to maintain the appropriate cylinder head temperature. The computer activates the EGR through two wires connected to an electrical solenoid. The EGR solenoid also contains a potentiometer that indicates the position of the EGR’s pintle, which is responsible for opening and closing the passage.
This operation is similar to dimming lights in a home. As the switch is turned, the lights get brighter with increased voltage. In this case, if the engine computer fails to detect any voltage change while attempting to open or close the EGR, it indicates that the EGR is stuck in one position. The codes P0490 EGR control circuit “A” and P0489 indicate no high or low voltage change, respectively, to indicate the EGR’s movement.
Unleaded fuel can produce Nox under extreme temperatures in the engine’s cylinders. The EGR recirculates a regulated amount of exhaust gas back into the intake manifold to dilute the incoming fuel mixture and reduce the cylinder head temperature below the threshold at which Nox forms.
EGR operation is essential for various reasons, including preventing Nox emissions, allowing more advanced timing for increased power without detonation, and enabling a leaner fuel mixture for improved fuel economy.
Symptoms
The symptoms experienced will depend on the position of the pintle in the EGR at the time of failure.
Potential Causes
The potential causes for this DTC may include:
Repair Procedures
If your vehicle has less than 100,000 miles, it is recommended to review your warranty. Most vehicles have an 80 or 100,000 mile warranty on emission controls. Additionally, you can search online for any relevant TSBs (technical service bulletins) related to these codes and their repair.
To perform these diagnostic procedures, you will need the following tools:
Open the hood and start the engine. If the engine has a rough idle, disconnect the plug on the EGR. If the engine smooths out, it indicates that the pintle is stuck in the EGR. Turn off the engine and replace the EGR.
Inspect the wire connector on the EGR. There are 5 wires, with the two outer wires supplying battery voltage and ground. The center three wires are the potentiometer used to signal the computer about the amount of EGR flow. The center terminal is the 5-volt reference terminal.
Thoroughly examine the connector for pushed out pins, corrosion, or bent pins. Also, closely inspect the wiring harness for any missing insulation or potential shorts. Look for any broken wires that could cause an open circuit.
A tip for repairing the EGR circuit without replacing the computer: Refer to the wiring diagram and locate the coolant temperature voltage reference terminal. Probe this terminal with the key on. If the 5-volt reference voltage is present, turn the key off and mark the two reference terminals used in these tests. Disconnect the computer’s connector, solder a jumper wire between these two terminals, and then reinstall the connector. This will allow the EGR to operate normally without replacing the computer.
Professional Service
While we always recommend seeking professional mechanical assistance to resolve this issue, if that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you are interested in this service, please upload your ECU file to our portal.
