|Trouble Code||Fault Location||Probable Cause|
|P0403||Exhaust gas recirculation (EGR) -circuit malfunction||Wiring, EGR solenoid, ECM|
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What Does Code P0403 Mean?
When a gasoline or diesel-powered vehicle runs, the fuel in the cylinder along with the oxygen in the air burns extremely hot. The gases produced in the combustion chamber are expelled in the exhaust stroke and sent through the exhaust pipe, destined for the atmosphere.
Unfortunately, fuel in the cylinders doesn’t burn completely. The unburned fuel is carried along with the exhaust as it exits the engine. These hydrocarbons are a major component of vehicle emissions and contribute to environmental pollution that can cause smog and exacerbate breathing issues.
In addition to unburned hydrocarbons in the exhaust gases, a particularly harmful byproduct of excessive engine heat is NOx. It is produced in a narrow range of temperatures at the upper limit of engine combustion.
The exhaust gas recirculation (EGR) system was developed to address these issues. The EGR system reintroduces a portion of the engine’s exhaust gases back into the combustion process. This achieves two things: completely burning the hydrocarbons in the exhaust gas as well as diluting the air in the combustion chamber to reduce ignition temperatures.
An EGR solenoid is used to meter the exhaust gases that are reintroduced into the engine. It also prevents the EGR system from operating until the engine is at operating temperature, otherwise the engine will run rough on startup as it starves for oxygen-rich air.
The EGR solenoid is typically mounted on the intake manifold. It uses engine vacuum to operate the EGR valve, which opens and closes to allow the exhaust gases into the intake. It receives 12-volt power from the powertrain control module when operating conditions — engine running and battery voltage above 12 volts — are met.
If the EGR solenoid circuit is not in the expected state when commanded by the PCM, DTC P0403 is set in the PCM and the Check Engine light is illuminated.
What are the common causes of code P0403 ?
- Defective EGR solenoid is most commonly found
- Lack of electrical signal to solenoid, usually short to ground
- EGR valve failure
- EGR valve or passage restriction
- Lack of vacuum, usually a vacuum leak
- PCM short
What are the symptoms of code P0403 ?
Symptoms vary depending on the position of the EGR solenoid circuit during malfunction. Symptoms may include:
- Check Engine light
- Rough run or misfire on startup, smoothing out as engine warms up.
- Rough run or misfire when engine hot, yet runs properly on startup.
- Hesitation to accelerate
- Fuel smell from exhaust
How do you troubleshoot code P0403 ?
Defective EGR Solenoid
The EGR solenoid can fail internally, either by cracking, spring failure, or otherwise. Usually if the EGR solenoid fails, it can easily be determined by removing the EGR solenoid and blowing air through the vacuum connections. When the EGR solenoid is removed, apply 12-volt power and ground to the solenoid. The vacuum passages should not be free-flowing. If you can blow through the valve, there is an internal failure and the EGR solenoid should be replaced.
Another way to check for a failed EGR solenoid is to disconnect the vacuum hose to the EGR valve while the engine is running cold. There should not be a change in the engine operation. If there is, it indicates a problem with the solenoid.
Lack of Electrical Signal to EGR Solenoid
The EGR solenoid is actuated with a 12-volt power source, switching the solenoid from the “leaking” position to a closed position when power is present. DTC P0403 most commonly indicates an electrical issue with the solenoid or the electrical connections.
You can check the electrical connections using a 12-volt test light and a DVOM. You’ll also need a vehicle-specific wiring diagram for the EGR solenoid circuit.
Poor wiring connection
The problem could be as simple as a poor connection to the EGR solenoid. Check for bent or broken terminals in the connector, or moisture or corrosion that can inhibit communication. Repair any problems and ensure the connector is fully seated and locked.
Short to voltage
Disconnect the two-wire harness from the EGR solenoid. With the key in the on position, connect one lead of the 12V test light to the negative battery terminal and probe the control circuit wire in the connector. If the tester lights up, there is a short to voltage on the control circuit. Trace the wire back to the PCM, checking for breaks, rubs, or corrosion on the wire that connect the circuit to power. Repair and retest.
If a short to voltage is present without a wiring problem, it’s possible the PCM has an inernal failure. Replace with a known good unit and retest.
Short to ground
Disconnect the control circuit from the EGR solenoid and the PCM. Test the control circuit using your DVOM, measuring resistance. If you have below 100 Ohms, there is a short to ground on the circuit. Trace the circuit for breaks or corrosion and repair.
Restriction in EGR Valve
The EGR valve operates by vacuum to open and close, allowing the exhaust gases to pass through. Restrictions can occur from carbon buildup especially, which is most notable in diesel engine applications. The restriction can either prevent the EGR valve from opening or, more commonly, restrict the valve from closing completely.
Remove the EGR valve to inspect for an obstruction. Some carbon buildup is normal but should not prevent moving parts from seating when fully closed. If there is buildup, clean it completely to ensure smooth movement, then reinstall.
EGR Valve Operation
With the engine off, apply a hand-pump vacuum tester to the EGR valve vacuum supply port. Build vacuum from 16 to 18 inches, monitoring the diaphragm for smooth movement throughout the range. The EGR valve should maintain vacuum while applied. If it does not, the EGR valve needs to be replaced. If the diaphragm doesn’t move smoothly or return to the fully closed position, the EGR valve should be replaced.
Lack of Vacuum
While not common, it’s possible that the engine is not producing the necessary vacuum to operate the EGR solenoid. You can check this with a vacuum gauge. Disconnect the vacuum supply line to the EGR solenoid and install the vacuum gauge. Start the engine and monitor the vacuum. Vacuum should build around 17 to 21 inches when at idle.
If vacuum does not build into that range while at idle, there is a vacuum leak present that needs to be addressed. Search for a hissing noise in the engine compartment as a loose or damaged vacuum hose or connection is typically to blame. Repair the vacuum leak and confirm operation.
Codes Related to P0403
- P0300 – Random/multiple cylinder(s) -misfire detected
- P0400 – Exhaust gas recirculation (EGR) system -flow malfunction
- P0401 – Exhaust gas recirculation (EGR) system -insufficient flow detected
- P0402 – Exhaust gas recirculation (EGR) system -excessive flow detected
- P0404 – Exhaust gas recirculation (EGR) system range/performance problem
- P0405 – Exhaust gas recirculation (EGR) valve position sensor A low input
- P0406 – Exhaust gas recirculation (EGR) valve position sensor A high input
- P0407 – Exhaust gas recirculation (EGR) valve position sensor B low input
- P0408 – Exhaust gas recirculation (EGR) valve position sensor B high input
- P0409 – Exhaust gas recirculation (EGR) sensor A circuit malfunction
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