Technical Description of OBD-II Trouble Code
The control circuit for Exhaust Gas Recirculation “A” is experiencing low voltage.
What does that mean?
This is a generic powertrain code that applies to all makes and models manufactured from 1996 onwards. However, the specific troubleshooting steps may vary depending on the vehicle.
These engine trouble codes indicate 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 the electrical solenoid. The EGR solenoid also contains a potentiometer that indicates the position of the EGR’s pintle, the mechanism 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. Codes P0489 EGR control circuit “A” indicate a lack of low voltage change to indicate EGR movement. P0490 is essentially the same, but it indicates a high voltage change instead of low.
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 reasons beyond preventing Nox emissions. It allows for more advanced timing, resulting in more power without detonation, and 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, check online for any relevant TSBs (technical service bulletins) related to these codes and their repair.
To perform these diagnostic procedures, the following tools will be required:
Open the hood and start the engine. If the engine idles roughly, 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. Inspect the wiring harness closely for any missing insulation or potential shorts. Look for 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 reconnect the connector. The EGR will operate normally without the need to replace the computer.
