Technical Description of OBD-II Trouble Code
The circuit for the Exhaust Gas Recirculation Sensor B is experiencing low voltage.
What does that mean?
This code is a generic powertrain code that applies to all makes and models of vehicles (1996-newer). However, the specific repair steps may vary slightly depending on the model.
EGR systems have different designs, but they all function in a similar way. The EGR valve is a valve controlled by the PCM (Powertrain Control Module) that allows a measured amount of exhaust gases to flow back into the cylinders to be burned with the air/fuel mixture. By injecting exhaust gas, which is an inert gas that displaces oxygen, back into the cylinder, combustion temperatures can be lowered, resulting in improved NOx (oxides of nitrogen) emissions.
EGR is not necessary during cold startup or at idle. It is commanded on under certain conditions such as startup, idle, partial throttle, or deceleration, depending on engine temperature and load. The EGR valve receives exhaust gases from an exhaust pipe or may be directly mounted in the exhaust manifold. When needed, 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.
EGR systems can be either electrically controlled or vacuum controlled. Electrically controlled EGR valves are directly controlled by the PCM through a wiring harness. Vacuum-controlled systems involve the PCM controlling a vacuum solenoid, which, when activated, allows vacuum to reach the EGR valve and open it. Both types of EGR valves may have an electrical connector for the feedback circuit, which allows the PCM to monitor the movement of the EGR valve pintle.
If the feedback circuit detects unusually low voltage or a lower position than commanded, the P0407 code may be set.
Note: The P0407 code is essentially the same as the P0405 code. The difference is that the P0405 DTC refers to the “A” sensor, while P0407 refers to the EGR “B” sensor. Consult a vehicle-specific repair manual to locate your “A” and “B” sensors.
Symptoms
Symptoms of a P0407 DTC may include:
Causes
Potential causes of a P0407 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 cause a valve to stick.
If the EGR valve does not respond to commands from the scan tool, disconnect the EGR harness connector. With the key in the on position and the engine off (KOEO), use a voltmeter to 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 read the EGR position as 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 EGR position reads 100 percent, check for poor terminal tension at the EGR valve connector. If the wiring is okay, replace the EGR valve.
Related EGR codes: P0400, P0401, P0402, P0403, P0404, P0405, P0406, P0408, P0409
