Low Value of Exhaust Gas Recirculation Control Circuit “A”
What Does It Mean?
This is a generic powertrain code, meaning it covers all makes/models from 1996 onward. However, specific troubleshooting steps vary by vehicle.
These engine fault codes refer to a failure in the EGR (Exhaust Gas Recirculation) system. More specifically—the electrical aspect. The EGR is an integral part of the vehicle’s emission system, designed to prevent the formation of harmful NOx (nitrogen oxides) in the cylinders.
The EGR is operated by the engine management computer. The computer opens or closes the EGR based on load, speed, and temperature to maintain the correct cylinder head temperature. There are two wires to the electric solenoid on the EGR that the computer uses to activate it. A potentiometer is also located in the EGR solenoid, which signals the position of the EGR pintle (the control mechanism that opens and closes the passage).
It works somewhat like dimming your lights at home. When the switch is turned, the lights get brighter as you increase the voltage. Your engine computer sees no voltage change while it attempts to open or close the EGR, indicating it is stuck in one position. Code P0489 EGR Control Circuit “A” means no low voltage change indicates the EGR is opening or closing. P0490 is essentially the same but refers to a high circuit as opposed to low.
Unleaded fuel is prone to producing NOx under extreme temperatures in the engine cylinders. The EGR routes a regulated amount of exhaust gas to the intake manifold. The purpose is to sufficiently dilute the incoming fuel mixture to lower the cylinder head temperature below that at which NOx forms.
EGR operation is essential for more reasons than preventing NOx emissions—it allows for more advanced timing for greater power without knocking and a leaner fuel mixture for better fuel economy.
Symptoms
Symptoms vary depending on the pintle’s position in the EGR at the time of failure.
Extremely rough engine operation
Check engine light on
Decreased fuel economy
Loss of power
No start or very hard starting followed by rough idle
Potential Causes
Causes
of this DTC may include:
Short to ground
Short to battery voltage
Bad connector with pushed-back pins
Corrosion in the connector
Clogged EGR pintle
Failed EGR solenoid
Faulty EGR
Defective ECU or computer
Repair Procedures
If your vehicle has less than 100,000 miles, it is advisable to check your warranty. Most vehicles have an 80,000 or 100,000-mile warranty on emission controls. Second, go online and check relevant TSBs (Technical Service Bulletins) related to these codes and their repair.
To perform these diagnostic procedures, the following tools will be needed:
Volt/Ohmmeter
EGR wiring diagram
Jumper wire
Two paper clips or sewing needles
Open the hood and start the engine. If the engine is idling, pull the plug on the EGR. If the engine smooths out, the pintle is stuck in the EGR. Stop the engine and replace the EGR.
Look at the wire connector on the EGR. There are 5 wires; the two outer wires provide battery voltage and ground. The three central wires are the potentiometer used to signal the computer the amount of EGR flow. The center terminal is the 5-volt reference terminal.
Carefully inspect the connector for pushed-back pins, corrosion, or bent pins. Examine the wiring harness closely for missing insulation or possible shorts. Look for broken wires that could cause an open circuit.
With the voltmeter, probe one of the end terminals with the red wire and ground the black wire. Turn the key on and look for 12 volts at both terminals.
If no voltage is displayed, there is a broken wire between the EGR and the ignition bus. If 12 volts appears on only one side, the EGR has an internal open. Replace the EGR.
Remove the connector from the EGR and with the key on and engine off, probe the two outer terminals for power. Note which one has 12 volts and reinstall the connector.
Place a paper clip in the end terminal that had no power; this is the ground terminal. Attach the jumper wire to the paper clip. Ground the jumper. There will be an audible “click” as the EGR is activated. Disconnect the ground wire and start the engine. Ground the wire again, and this time the engine will start to run rough when the EGR is powered and smooth out when the ground is removed.
If the EGR clicked and made the engine run rough, the EGR is good; the problem is electrical. Otherwise, stop the engine and replace the EGR.
Probe the center terminal on the EGR connector. Turn the key. There should be 5.0 volts displayed if the computer is working correctly. Turn the key off.
Use the EGR wiring diagram and locate the “EGR Reference Voltage” terminal on the computer. Place a pin or paper clip in the computer connector at this point to probe the terminal again.
Turn the key. If 5 volts is present, the computer is good and the problem is in the EGR harness. If no voltage is present, the computer is faulty.
A tip for repairing the EGR circuit without replacing the computer: Look at 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 there, turn the key off and mark the two reference terminals used in these tests. Pull the computer connector, solder a jumper between these two terminals. Install the connector and the EGR will operate normally without replacing the computer.