Technical Description of OBD-II Trouble Code
Low Circuit in Exhaust Gas Recirculation Sensor A
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
There are various designs of Exhaust Gas Recirculation (EGR) systems, but they all function in a similar manner. The EGR valve is a valve controlled by the Powertrain Control Module (PCM) that allows a measured amount of exhaust gases to flow back into the cylinders to be burned with the air/fuel mixture. By reintroducing exhaust gas, which is an inert gas that displaces oxygen, into the cylinder, combustion temperatures can be lowered, thereby helping to reduce NOx (oxides of nitrogen) emissions.
EGR is not necessary during cold startup or at idle. EGR is activated under specific conditions such as startup or at idle, partial throttle, or deceleration, depending on engine temperature and load. Exhaust gases are supplied to the EGR valve from an exhaust pipe, or the EGR valve may be directly mounted in the exhaust manifold. When required, the valve is commanded to open, allowing the gases to enter the cylinders. Some systems divert exhaust gases directly into the cylinders, while others inject them into the intake manifold, from where they are pulled into the cylinders.
Some EGR systems are simple, while others are more complex. Electrically controlled EGR valves are directly controlled by the PCM. A wiring harness connects to the valve itself, and the PCM commands it based on the need. These valves can have 4 or 5 wires, typically including 1 or 2 grounds, a 12-volt ignition feed, a 5-volt reference circuit, and a feedback circuit. Other systems are vacuum controlled, which are relatively simple. The PCM controls a vacuum solenoid that, when activated, allows vacuum to reach the EGR valve and open it. This type of EGR valve usually has an electrical connector for the feedback circuit. The EGR system’s feedback circuit enables the PCM to determine if the EGR valve pintle is moving as it should. If the feedback circuit detects unusually low voltage or a lower position than commanded, it may trigger the P0405 code.
Symptoms
Symptoms of a P0405 DTC may include:
Causes
Possible causes of a P0405 code include:
Possible Solutions
If you have access to a scan tool, you can command the EGR valve to open. If it responds and the feedback indicates that the valve is moving properly, the problem may be intermittent. In cold weather, moisture can freeze in the valve, causing it to stick. After the vehicle warms up, the problem may disappear. Carbon or other debris can also get lodged in the valve, causing it to stick.
If the EGR valve does not respond to your commands using the scan tool, disconnect the EGR harness connector. Turn the key to the on position, with the engine off (KOEO). Using a voltmeter, check for 5 volts on the reference wire to the EGR valve. If there is no 5 volts, check if there is any voltage at all. If there is 12 volts, repair the short to voltage in the 5-volt reference circuit. If there is no voltage, connect a test light to battery voltage and probe the 5-volt reference wire. If the test light illuminates, the 5-volt reference circuit is shorted to ground. Repair as necessary. If the test light does not illuminate, check for an open in the 5-volt reference circuit. Repair as necessary.
If there is no apparent problem and there is no 5-volt reference, the PCM may be at fault. However, other codes will likely be present. If 5 volts are present on the reference circuit, jumper the 5 volts to the EGR signal circuit. The scan tool should now display an EGR position of 100 percent. If it does not, connect a test light to battery voltage and probe the EGR signal circuit. If it illuminates, the signal circuit is shorted to ground. Repair as necessary. If the light does not illuminate, check for an open in the EGR signal circuit. Repair as necessary.
If, after jumpering the 5-volt reference circuit to the EGR signal circuit, the scan tool displays an EGR position of 100 percent, check for poor terminal tension at the EGR valve connector. If the wiring is fine, replace the EGR valve.
Related EGR codes: P0400, P0401, P0402, P0403, P0404, P0406, P0407, P0408, P0409
