Technical Description of OBD-II Trouble Code
The circuit for Exhaust Gas Recirculation Sensor A is registering a high voltage.
What does that mean?
This code is a generic powertrain code that applies to all vehicle makes and models manufactured from 1996 onwards. However, the specific repair steps may vary slightly depending on the model.
The Exhaust Gas Recirculation (EGR) system is designed to reduce combustion temperatures under certain conditions, thereby decreasing the emissions of Nitrogen Oxides (NOx). It achieves this by recirculating inert exhaust gases back into the cylinder to be burned with the air/fuel mixture. Inert exhaust gas burns at a slower rate and lowers the combustion temperatures. The EGR valve, which is controlled by the computer, opens to allow the flow of exhaust gas into the cylinders.
The EGR valve may be operated by vacuum. In such cases, a Powertrain Control Module (PCM) controlled EGR vacuum solenoid is used to deliver vacuum to the EGR valve. When activated by the PCM, the EGR solenoid opens, allowing engine vacuum to reach the EGR valve. This engine vacuum opens the valve, enabling the passage of exhaust gases into the combustion chamber. Other EGR valves are electronic and directly controlled by the PCM. The PCM activates solenoids that are integrated into the EGR valve. These solenoids open for varying durations, allowing the necessary amount of exhaust to pass through. The EGR system is continuously monitored for faults. Most EGR valves have a feedback sensor that informs the computer about the actual position of the EGR valve. This sensor typically provides a voltage reading between 0.4 and 5 volts.
If the EGR position sensor maintains an abnormally high reading for an extended period, this code may be triggered.
Symptoms
The symptoms associated with a P0406 DTC may include:
Causes
The potential causes of a P0406 code are:
Possible Solutions
If the vehicle starts and stalls or fails to run with this code present, try disconnecting the EGR valve and then restarting the engine. If this does not make a difference, remove the EGR valve and inspect it for any debris. Clean the valve and reinstall it. If the problem persists, block off the EGR port and attempt to start the engine. If the engine starts under these conditions, it indicates that the EGR valve is stuck open and needs to be replaced. If unplugging the PCM controlled EGR valve allowed the engine to restart, there is likely a wiring issue, possibly a short circuit that is keeping a solenoid open.
Using a scan tool, check the EGR position on the datastream with the Key on Engine running and compare it with the desired EGR position. If the reading is normal, suspect an intermittent problem. If it shows 5 volts or higher, inspect the EGR sensor signal circuit for a short circuit to the 5 volt reference wire or to B+. Repair any issues as necessary. Also, ensure that there is a good ground path on the ground circuit. Repair any open circuits or short circuits in the ground circuit.
For a vacuum controlled EGR valve with an EGR solenoid, if unplugging the EGR valve vacuum source allows the engine to start, suspect a faulty EGR solenoid that is allowing vacuum to reach the EGR valve constantly. Replace the EGR solenoid as needed. If this code is present and the engine starts and runs normally, suspect an open circuit in the wiring. Inspect and repair any wiring problems. If the wiring checks out, replace the EGR valve. If there are issues with the wiring to and from the EGR valve
Related EGR codes: P0400, P0401, P0402, P0403, P0404, P0405, P0407, P0408, P0409
P0406 Diagnosis Video
Note: We are not affiliated with the producers of the following video. We are including it here as an additional troubleshooting tool, it may or may not apply to your vehicle issue.
