P0405 - EGR SENSOR A CIRCUIT LOW

Although there are several designs of EGR (Exhaust Gas Recirculation) systems, they all work similarly. The Exhaust Gas Recirculation (EGR) valve is controlled by the PCM (Powertrain Control Module) and in this way, the amount of exhaust gas, which is to be burned with the air/fuel mixture, can be measured. As this gas is very inert and displaces oxygen, when it is injected back into the cylinder, it helps to reduce temperature and nitrogen oxide emission.

The Exhaust Gas Recirculation (EGR) valve and the PCM are connected directly to each other electrically via a group of wires, usually 4 or 5 wires. Two of these are 12-volt ignition power cables, one for a 5-volt reference circuit, and one for a feedback circuit. The feedback circuit allows the Powertrain Control Module (PCM) to observe that the EGR valve clamp is performing its movements correctly. If the feedback loop detects that the voltage is low or the position it has commanded is not correct, the fault code P0405 OBD2 is set.

• The service light (Check Engine) is on.
• The engine may be unstable.

A P0405 code may have one or more of the following problems:

• There may be a short circuit to the ground of the EGR (Exhaust Gas Recirculation) reference signal.
• The voltage in the ground circuits or reference signals may be short-circuited.
• Perhaps, the Exhaust Gas Recirculation (EGR) valve is defective.
• Some PCM (Powertrain Control Module) cables may be subject to friction or wear, and some terminals may be loose.

To solve the diagnostic code P0405, you can check the following components:

• With a scan tool, you can command the EGR valve and check its response. If it moves, it indicates that the problem may be due to factors such as weather or humidity, as they cause the valve to stick. After the vehicle heats up, the problem may disappear. Similarly, there may be an element such as carbon, which causes it to stick as well.
• If the valve does not respond to the commands of the scan tool, disconnect the connector from the EGR (Exhaust Gas Recirculation) cables. Then, turn the ignition switch, and using a voltmeter. Make sure there are 5 volts on the reference wire to the Exhaust Gas Recirculation valve. If there are no 5-volt reference, check for 12 volts. Repair the short circuit to voltage in the 5-volt reference circuit.
• If no voltage is present, connect a voltage test light to the battery and the probe of the 5-volt reference cable. If this test light comes on, it indicates that the 5-volt reference circuit is shorted to ground. Repair it as necessary.
• If the 5-volt reference is present, make a connection of the 5-volt to the EGR signal circuit, the position of the EGR valve should change in the scan tool indicating that it is at 100%. Check that the voltage is not low at the EGR valve connector terminal. Repair it or replace it if necessary.
• Replace the EGR (Exhaust Gas Recirculation) valve.