P0490 Exhaust Gas Recirculation (EGR) "A" Control Circuit High

OBD-II Trouble Code - P0490 - Data Sheet

Exhaust Gas Recirculation Control Circuit "A" High

What does trouble code P0490 mean?

This is a generic transmission code which means it covers all makes / models from 1996 onwards. However, specific troubleshooting steps may differ from vehicle to vehicle.

These engine trouble codes refer to a malfunction in the exhaust gas recirculation system. More specifically, the electrical aspect. The exhaust gas recirculation system is an integral part of the vehicle exhaust system, the function of which is to prevent the formation of harmful NOx (nitrogen oxides) in the cylinders.

EGR is controlled by the engine management computer. The computer opens or closes the exhaust gas recirculation depending on load, speed and temperature in order to maintain the correct cylinder head temperature. There are two wires to the electrical solenoid on the EGR that the computer uses to activate it. The potentiometer is also located in the exhaust gas recirculation solenoid, which signals the position of the EGR rod (the operating mechanism that opens and closes the duct).

This is very similar to dimming the lights in your home. When you turn the switch, the light becomes brighter as the voltage increases. Your engine computer does not see any voltage change when it tries to open or close the EGR, indicating that it is stuck in one position. P0490 Exhaust Gas Recirculation Control Circuit A means there is no high voltage change, indicating that the EGR is opening or closing. P0489 is basically identical, but it means circuit low, not high.

Unleaded fuel tends to form NOx at extreme engine cylinder temperatures. The EGR system directs a controlled amount of exhaust gas back to the intake manifold. The goal is to dilute the incoming fuel mixture sufficiently to bring the cylinder head temperature below that at which NOx is formed.

The operation of the EGR system is important for more reasons than NOx prevention - it provides more accurate timing for more power without knocking, and a leaner fuel mixture for better fuel economy.

Symptoms

Symptoms will vary depending on the position of the EGR needle at the time of failure. In most cases, the code P0490 is not preceded by any symptoms. Vehicle owner will be alerted to the problem by the Check Engine light coming on. However, some vehicles may run erratically or be difficult to start. Vehicle owners can there is a decrease in power or a decrease in fuel consumption.

• Extremely rough running engine
• Check engine light is on
• Falling fuel economy
• Decrease in power
• No start or very difficult to start followed by a sharp idle

Possible Causes of Code P0490

Most often, a clogged EGR or DPFE channel is to blame for the P0490 code.

There may also be a short to battery voltage or an ECU malfunction causing this code.

Reasons for this DTC may include:

• Short circuit to ground
• Short circuit to battery voltage
• Bad connector with pushed out pins
• Corrosion in the connector
• Dirty EGR needle
• Faulty exhaust gas recirculation solenoid
• Bad EGR
• Defective ECU or computer

Repair procedures

If your vehicle has traveled less than 100,000 80 miles, it is recommended that you review your warranty. Most vehicles carry a 100,000 or XNUMX miles emission control warranty. Second, go online and check all relevant TSBs (Technical Service Bulletins) related to these codes and how to repair them.

To perform these diagnostic procedures, you will need the following tools:

• Volt / Ohmmeter
• Exhaust gas recirculation connection diagram
• Jumper
• Two paper clips or sewing needles

Open the hood and start the engine. If the engine does not idle well, remove the plug from the EGR system. If the engine smooths, the pin gets stuck in the EGR. Stop the engine and replace the EGR.

Look at the wire connector on the EGR. There are 5 wires, the outer two wires feed the battery voltage and ground. The three center wires are a potentiometer that signals to the computer the amount of EGR flow. The center terminal is the 5V reference terminal.

Thoroughly inspect the connector for knocked out pins, corrosion, or bent pins. Inspect the wiring harness carefully for any insulation or possible short circuits. Look for open wires that could open the circuit.

• Use a voltmeter to test any terminal lead with the red wire and ground the black wire. Turn on the key and find 12 volts and both end terminals.
• If the voltage is not displayed, then there is an open wire between the EGR system and the ignition bus. If 12 volts is displayed on one side only, the EGR system has an internal open circuit. Replace EGR.
• Disconnect the connector from the exhaust gas recirculation system and with the key on and the engine off, check both external contacts for power. Write down which one has 12 volts and replace the connector.
• Place a paper clip on the terminal lug that was not powered, this is the ground lug. Attach a jumper to a paperclip. Ground the jumper. A “click” will be heard when the EGR is activated. Disconnect the ground wire and start the engine. Ground the wire again and this time the engine will run rough when the EGR is energized and flatten when ground is removed.
• If the EGR system is activated and the engine starts to work intermittently, then the EGR system is in order, the problem is electrical. If not, stop the engine and replace the EGR.
• Check the center terminal of the exhaust gas recirculation connector. Turn on the key. If the computer is working properly, 5.0 volts is displayed. Turn off the key.
• Refer to the EGR wiring diagram and locate the EGR voltage reference terminal on the computer. Insert a pin or paper clip into the connector on the computer at this point to check the contact back.
• Turn on the key. If 5 volts is present, the computer is OK and the problem is in the wiring harness to the EGR system. If there is no voltage, then the computer is faulty.

Advice for repairing the exhaust gas recirculation circuit without replacing the computer: Look at the wiring diagram and locate the coolant temperature reference voltage terminal. Check this terminal with the included key. If the 5 volt ref. Voltage is present, turn off the key and mark the two support terminals used in these tests. Pull out the computer connector, solder a jumper wire between these two pins. Install the connector and the EGR system will work normally without replacing the computer.

Common Mistakes When Diagnosing Code P0490

The most common mistake when diagnosing the cause of a code P0490 is to automatically replace the EGR valve. This part does not break down as often as many others. components of the EGR system.

How serious is the P0490 code?

Because the accumulation of NOx in a car's cylinders can be very harmful, the presence of Code P0490 is very serious. A properly functioning EGR is also a key component for good fuel economy. This repair should be addressed immediately.

What repairs can fix code P0490?

Making sure that the electrical components are not responsible for storage

Code P0490, the mechanic has several repair options:

• Use a scanner to monitor the EGR function and manually compare the information with manufacturer's specifications.

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

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

• Remove the EGR valve and clean it of blockage.
• Make sure the computer is working properly and replace it if necessary.
• Check all connectors and wiring for PCM and repair or replace as needed.

After each such repair, the code must be cleared and the system must be rechecked. The more repairs will be marked in the list, the easier it will be specialist to narrow down the true cause of the code P0490.

Additional comments to consider regarding code P0490

If code P0490 is found on a vehicle with less than 100 miles, check Manufacturer's Warranty or Dealer's Warranty. The EGR system is normally closed under the standard warranty, and the cost of replacement or repair may be covered guarantee.

P0490 ✅ SYMPTOMS AND CORRECT SOLUTION ✅ - OBD2 Fault Code

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