Technical Definition:

Secondary Air Injection System Switching Valve A Circuit Open

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Technical Definition:

Exhaust Gas Recirculation (EGR) (Sensor A) Circuit High

Technical Description:

Possible Causes:

• EGR sensor signal circuit shorted to B+ (battery voltage)
• EGR sensor signal circuit shorted to the 5 volt reference circuit to EGR
• EGR sensor ground circuit open
• EGR sensor signal circuit open
• Bad EGR (internal failure on EGR sensor or solenoid)
• Debris caught in valve and holding it open or closed

Possible Symptoms:

• Increase in combustion temperatures (and NOx emissions)
• MIL (Malfunction indicator lamp) illumination
• Possible surging while driving
• Possible intermittent stall

Possible Solutions:

If the vehicle starts and stalls or will not run with this code present, try unplugging the EGR valve and then restarting. If this makes no difference, remove the EGR valve and inspect for debris. Clean and reinstall. If this still doesn’t fix the problem, block off EGR port and attempt to start the engine. If this allows the engine to start, the EGR valve is stuck open and needs replaced. If unplugging the PCM controlled EGR valve allowed the engine to restart then there is likely a wiring problem, possibly a short holding a solenoid open.

Using a scan tool, view the EGR position on the datastream with the Key on Engine running and compare with the EGR desired position. If it reads normal, suspect an intermittent problem. If it shows 5 volts or higher, check the EGR sensor signal circuit for a short to the 5 volt reference wire or to B+. Repair as needed. Also check that there is a good ground path on the ground circuit. Repair any opens or shorts on ground circuit

On a vacuum controlled EGR valve with EGR solenoid: if unplugging the EGR valve vacuum source allows the engine to start, then suspect a bad EGR solenoid allowing vacuum to the EGR valve all the time. Replace the EGR solenoid as needed. If this code is present and your engine starts and runs just fine, suspect an open in the wiring. Inspect and repair any wiring problems. If the wiring checks out, replace the EGR valve. If the wiring to and from the EGR valve

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Technical Definition:

Exhaust Gas Recirculation (EGR) (Sensor B) Circuit Low

Technical Description:

Possible Causes:

• Short to ground in EGR signal or Reference circuits
• Short to voltage in EGR ground or signal circuits
• Bad EGR valve
• Bad PCM wiring issues due to chafing or loose terminals

Possible Symptoms:

• MIL (Malfunction Indicator Lamp) illumination

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Technical Definition:

Exhaust Gas Recirculation (EGR) (Sensor B) Circuit High

Technical Description:

The EGR (Exhaust gas recirculation) system is designed to lower combustion temperatures under certain conditions, thereby reducing oxides of Nitrogen (NOx) emissions. It does this by recirculating inert exhaust gasses back into the cylinder to be burned with the air/fuel mixture. Inert exhaust gas burns slower and lowers the temperatures of combustion. The EGR valve is computer controlled and opens to allow the exhaust gas to flow into the cylinders.

Possible Causes:

• EGR sensor signal circuit shorted to B+ (battery voltage)
• EGR sensor signal circuit shorted to the 5 volt reference circuit to EGR
• EGR sensor ground circuit open
• EGR sensor signal circuit open
• Bad EGR (internal failure on EGR sensor or solenoid)
• Debris caught in valve and holding it open or closed

Possible Symptoms:

• Increase in combustion temperatures (and NOx emissions)
• MIL (Malfunction indicator lamp) illumination
• Possible surging while driving
• Possible intermittent stall

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Technical Definition:

Exhaust Gas Recirculation (EGR) (Sensor A) Circuit Malfunction

Technical Description:

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Technical Definition:

Exhaust Gas Recirculation (EGR) Control Circuit Range / Performance

Technical Description:

The EGR (Exhaust Gas Recirculation) system’s purpose is to redirect exhaust gas back into the cylinders. Since exhaust gas is inert, it displaces oxygen and fuel, thereby lowering cylinder temps, which, in turn, lowers oxides of nitrogen emissions. For that reason it needs to be carefully metered into the cylinders (via the EGR valve) so as not to adversely affect the engine’s performance. (Too much EGR and the engine won’t idle).

Possible Causes:

• Open or short in the 5 Volt reference circuit
• Open or short in the ground circuit
• Open or short in the PCM controlled voltage circuit
• Bad PCM (less likely)

Possible Symptoms:

There may be no symptoms of a P0404 obd code other than the MIL (malfunction indicator lamp) or check engine light. However, Exhaust Gas Recirculation systems are inherently problematic due to carbon buildup in the intake manifold, etc. This normal buildup can lodge in an EGR valve, holding it open when it should be closed. If this is the case, the engine may idle rough, or not at all. If the valve has failed and is NOT opening, then symptoms would be higher combustion temps and as a result, higher Nox emissions. But the latter symptoms aren’t going to be noticeable to a driver.

Exhaust Gas Recirculation Circuit Range/Performance

Possible Solutions:

• Using a scan tool command the EGR valve to open while watching the actual EGR position (it will probably be labeled “desired EGR” or something similar). The actual EGR position should be very close to the “desired” EGR position. If it is, then the problem is likely intermittent. It may have been a lodged piece of carbon that has since dislodged, or it could be a bad EGR valve winding that intermittently opens or shorts as the valve temperature changes.
• If the EGR “desired” position is not close to the “actual” position, then unplug the EGR sensor. Check for a good 5 Volt reference voltage to the connector. If it doesn’t show a reference voltage, repair an open or short in the 5 Volt reference circuit.
• If there is a 5 volt reference voltage, activate the EGR with the scanner, monitor the EGR ground circuit with a DVOM (Digital Volt/Ohm meter). It should indicate a good ground. If it doesn’t then repair the ground circuit.
• If there is a good ground, then check the control circuit. It should indicate voltage that varies according to the percentage that the EGR is open. As it’s open more, the voltage should increase accordingly. If it does, then replace the EGR valve.
• If the voltage doesn’t increase incrementally, then repair open or short in EGR control circuit.

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– EGR volume control solenoid valve
– EGR volume control solenoid valve harness is open or shorted
– EGR volume control solenoid valve circuit poor electrical connection
– EGR temperature sensor and circuit

Specific Makes:

– Engine hesitation

Technical Definition:

Exhaust Gas Recirculation (EGR) (Sensor A) Circuit Low

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Technical Definition:

Exhaust Gas Recirculation (EGR) Flow

Technical Description:

The exhaust gas recirculation (EGR) valve is vacuum controlled valve that regulates the amount of exhaust gases that re-enter the cylinders.

Possible Causes:

• Plugged EGR passage which restricts the flow of exhaust gasses
• Faulty EGR solenoid
• Faulty EGR solenoid wiring/harness
• Vacuum lines damaged/disconnected to the EGR valve solenoid or to the EGR valve
• Faulty EGR valve

Possible Symptoms:

Exhaust Gas Recirculation Flow Malfunction

Possible Solutions:

• Using a scan tool, operate the EGR valve with the engine running. If the engine stumbles, the problem was likely intermittent wiring problem or intermittent blockage problem
• If engine doesn’t stumble, operate the EGR valve manually, if possible. If engine doesn’t stumble and die, the ports are likely plugged. Removal of valve and cleaning of all ports will be required
• Checking of solenoid can only usually be done with a scan tool, because most solenoids operate with a duty cycle of voltage, rather than constant voltage
• Check all vacuum lines, hoses, etc for any damage
• Visually inspect the solenoid harness and the solenoid for damage
• Replace EGR valve

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Exhaust Gas Recirculation (EGR) volume control valve stuck closed
– Faulty Exhaust Gas Recirculation (EGR) volume control solenoid valve
– Faulty EGR Valve
– Faulty EGR temperature sensor and circuit
– Exhaust Gas Recirculation (EGR) solenoid valve harness is open or shorted
– Exhaust Gas Recirculation (EGR) solenoid valve circuit poor electrical connection
– Dead (Weak) battery

Specific Makes:

– Possible engine hesitation

Technical Definition:

Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

Technical Description:

EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR.

Possible Causes:

• The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
• There is a blockage in the EGR (tube), most likely carbon buildup
• The EGR valve is faulty
• The EGR valve may not be opening due to a lack of vaccuum

Possible Symptoms:

Exhaust Gas Recirculation Flow Insufficient Detected

Possible Solutions:

• Use a vacuum pump and pull the EGR valve open while monitoring engine RPM’s & DPFE voltage. There should be a noticable difference in RPM’s with the EGR open
• Clean out the EGR valve and/or tubing to remove deposits
• Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
• Replace the DPFE sensor (with a good quality / OEM one)
• Replace the EGR valve

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– EGR passage clogged
– Faulty EGR Vacuum Modulator Valve
– Faulty EGR Valve
– Faulty EGR solenoid valve
– EGR solenoid valve harness is open or shorted
– EGR solenoid valve circuit poor electrical connection
– Dead (Weak) battery
– Faulty EGR temperature sensor and circuit
– Exhaust gas leaks

Specific Makes:

– Possible engine hesitation

Technical Definition:

Exhaust Gas Recirculation (EGR) Flow Excessive Detected

Technical Description:

EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen.

Possible Causes:

• DPFE (differential pressure) sensor is faulty and needs to be replaced
• There is a blockage in the EGR (most likely carbon buildup)
• EGR valve fault
• EGR valve may not be opening due to a lack of vaccuum

Possible Symptoms:

Exhaust Gas Recirculation Flow Excessive Detected

Possible Solutions:

• Check the voltage at the DPFE sensor both at idle and when the EGR is open
• Replace the DPFE sensor

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– EGR volume control valve stuck open
– Faulty EGR volume control valve
– EGR solenoid valve harness is open or shorted
– EGR solenoid valve circuit poor electrical connection
– Faulty EGR temperature sensor and circuit

Specific Makes:

– Possible engine hesitation

Technical Definition:

Exhaust Gas Recirculation (EGR) Control Circuit

Technical Description:

The Exhaust Gas Recirculation (EGR) system is controlled by a vacuum solenoid. The solenoid is supplied ignition voltage. The Powertrain Control Module (PCM) controls the vacuum solenoid by grounding the control circuit(ground) or driver

Possible Causes:

• Bad EGR solenoid
• Excessive resistance in control circuit (PCM controlled ground) due to an open, chafing or damage to the harness
• Poor connection at the EGR solenoid harness (worn or loose pins)
• Water intrusion at the EGR solenoid harness
• Blockage in EGR control solenoid holding solenoid open or closed causing excessive resistance
• Loss of supply voltage to EGR solenoid
• Bad PCM

Possible Symptoms:

Exhaust Gas Recirculation Circuit Malfunction

Possible Solutions:

With the ignition on and engine off, use a scan tool to activate the EGR solenoid. Listen or feel for a clicking, indicating that the solenoid is operating.

If the solenoid does operate, you’ll have to check current draw on the ground circuit. It should be less than one amp. If it is then the problem is intermittent. If it isn’t then there is excessive resistance in the circuit and perform the following

• When it’s activated see if you can blow lightly through it. IF you can’t there may be a blockage causing excessive resistance. Replace EGR solenoid as needed. If there is no blockage, disconnect the EGR solenoid and the PCM connector containing the EGR solenoid control circuit. Using a digital Volt-Ohm meter (DVOM) check resistence between the control circuit and battery ground. It should be infinite. If it isn’t, then there is a short to ground on the control circuit. Repair the short to ground and retest as needed.
• If the solenoid doesn’t click as it should, disconnect the EGR solenoid connector and connect a test light between the two wires. Using the scan tool, command the EGR solenoid on. The light should light up. If it does, replace the EGR solenoid. If it does not perform the following: a. Check for 12 Volts on the ignition supply voltage to the solenoid. If it isn’t present, inspect the supply circuit for an open, or a short due to chafing or breakage and re-test. b. If it still doesn’t operate: then manually ground the EGR solenoid control circuit. The light should light. If it does, repair open in EGR solenoid control circuit and re-test. If it doesn’t, replace EGR solenoid.

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Faulty EGR volume control solenoid valve
– EGR volume control solenoid valve harness is open or shorted
– EGR volume control solenoid valve circuit poor electrical connection
– EGR temperature sensor and circuit

Specific Makes:

– Possible engine hesitation