What does it mean?
This is a generic powertrain diagnostic trouble code (DTC), meaning it covers all makes/models from 1996 onward. However, specific troubleshooting steps vary by vehicle.
The OBD-II trouble code P046C is a generic diagnostic code related to a range/performance issue in the exhaust gas recirculation (EGR) valve electrical circuit “A”.
The purpose of the EGR valve is to introduce a regulated amount of exhaust gas into the intake manifold. The goal is to keep cylinder head temperatures below 2500°F. Oxygen nitrates (NOx) form when temperatures exceed 2500°F. NOx is responsible for smog and air pollution.
The control computer—either the Powertrain Control Module (PCM) or Engine Control Module (ECM)—has detected an abnormally low, high, or non-existent signal voltage. Refer to a manufacturer-specific repair guide to determine which sensor is “A” for your exact vehicle.
EGR Operating Principles
The P046C trouble code refers to the same issue across all vehicles; however, there are many types of EGR systems, sensors, and activation methods. The only similarity is that they all route exhaust gases into the intake manifold to cool cylinder head temperatures.
Introducing spent exhaust gases into the engine at the wrong time reduces power and causes rough idling or stalling. With this in mind, the computer programming only opens the EGR when engine RPM is above 2000 and closes it under load.
Symptoms
Symptoms depend on the EGR pintle position at the time of failure.
The service engine soon light will illuminate, and OBD code P046C will be set. Additionally, a second code related to EGR sensor failure may be set. Code P044C relates to low sensor voltage, and P044D relates to high voltage.
If the EGR pintle is stuck partially open, the vehicle may not idle well or may stall.
Engine knocking may be heard under load or at high RPM.
No symptoms at all.
Potential Causes
- Faulty EGR sensor “A”
- Defect in the sensor wiring harness
- EGR pintle stuck in closed position, with carbon buildup preventing it from opening
- Lack of vacuum at the EGR solenoid
- Faulty EGR solenoid
- Faulty EGR position sensor
- Faulty EGR differential pressure feedback sensor.
Repair Procedures
All EGR valves have one thing in common: they recirculate exhaust from the exhaust system to the intake manifold. Beyond that, they differ in their methods of regulating pintle opening and detecting its position.
The following repair procedures address the most common issues responsible for the majority of EGR system failures. Wiring harness or sensor failures require a service manual to determine proper wire identification and diagnostic procedures.
Keep in mind that wiring differs between manufacturers, and computers do not respond well if the wrong wire is probed. If you probe the wrong wire and send excessive voltage through the computer’s sensor input terminal, the computer may be damaged.
Similarly, if the wrong connector is unplugged, the computer could lose its programming, requiring the vehicle to be towed to a dealer for reprogramming.
Code P046C indicates a malfunction in circuit “B”, so check the EGR sensor connector for corrosion, bent or pushed-out terminals, or loose connections. Clean any corrosion and reinstall the connector.
Disconnect the electrical connector and remove the EGR valve. Check for carbon buildup in the EGR’s intake and exhaust passages. Clean any carbon deposits as needed so the pintle moves up and down smoothly.
Inspect the vacuum line from the EGR to the solenoid and replace it if defects are found.
Check the solenoid’s electrical connector for corrosion or damage.
If the vehicle is a Ford, trace the two vacuum hoses from the EGR to the differential pressure feedback EGR (DPFE) sensor at the rear of the manifold.
Check both pressure hoses for corrosion. Experience shows these hoses can clog with exhaust carbon. Use a small pocket screwdriver or equivalent to clean the hoses of corrosion, and the sensor should resume functioning.
If the most common tests do not resolve the issue, a service manual is needed to continue testing the wiring circuits. The best solution is to take the vehicle to a service center with the proper diagnostic equipment. They can quickly identify and repair this type of problem.