Do I need a new EGR valve?
Senior Member
Joined: Jan 2024
Posts: 641
From: Davison, MI
HERE'S THE TREE FOR THE P0401 CODE. NOTICE THE FIRST THING IS TO DO THE P0405 FIRST.
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Home >> Saturn >> 1999 >> SL L4-1.9L SOHC VIN 8 >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0401
April 5, 2026: LEMON Manuals is launched! Read the announcement.
The linear EGR system consists of a linear EGR valve, the PCM and its associated wiring. The PCM directly controls the ground for the EGR valve when certain conditions have been met. Voltage is supplied by the UHJB to the EGR valve when the ignition is turned On. When the PCM grounds the valve, a diagnostic feedback signal can determine if the valve had actually moved. Since the correct feedback voltage is possible, but the passage has restricted flow, P0401 was implemented.
DTC PARAMETERS
EGR flow restrictions are diagnosed during a deceleration. The EGR valve is commanded closed during a normal deceleration. To run the P0401 test the valve is opened during deceleration and a change in MAP is expected. If the change is MAP is below a threshold it indicates flow is restricted.
DTC P0401 will set if a calculated value compared to an engine speed vs barometric pressure determines there is a restriction in EGR flow when:
^ Engine speed is between 1350-2000 rpm.
^ VSS is greater than 48 km/h (30 mph).
^ Throttle is closed.
^ Engine coolant temperature is greater than 70°C (150°F).
^ Vehicle is in top gear.
^ No EGR pintle, TP Sensor, MAP, VSS, IAT, ECT or IAC DTCs have been set.
IMPORTANT: The EGR flow insufficient test is checked once per ignition cycle during deceleration.
DIAGNOSTIC AIDS
The Scan tool can read the number of deceleration test that have been performed since the DTCs were cleared. The Scan tool also displays the EGR decel average value as well as the FAIL threshold when the DTC will set. The average must be greater than the threshold to set P0401.
^ Carbon buildup around the EGR pintle valve bore opening may restrict exhaust gas flow. Build-up of carbon in the EGR passages will result in P0401.
^ Diagnose the other DTCs listed under parameters, especially a MAP sensor DTC before diagnosing P0401.
scientia non olet · About LEMON Manuals
LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Saturn >> 1999 >> SL L4-1.9L SOHC VIN 8 >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0401
April 5, 2026: LEMON Manuals is launched! Read the announcement.
P0401
Diagnostic Chart:
Wiring Diagram:
The linear EGR system consists of a linear EGR valve, the PCM and its associated wiring. The PCM directly controls the ground for the EGR valve when certain conditions have been met. Voltage is supplied by the UHJB to the EGR valve when the ignition is turned On. When the PCM grounds the valve, a diagnostic feedback signal can determine if the valve had actually moved. Since the correct feedback voltage is possible, but the passage has restricted flow, P0401 was implemented.
DTC PARAMETERS
EGR flow restrictions are diagnosed during a deceleration. The EGR valve is commanded closed during a normal deceleration. To run the P0401 test the valve is opened during deceleration and a change in MAP is expected. If the change is MAP is below a threshold it indicates flow is restricted.
DTC P0401 will set if a calculated value compared to an engine speed vs barometric pressure determines there is a restriction in EGR flow when:
^ Engine speed is between 1350-2000 rpm.
^ VSS is greater than 48 km/h (30 mph).
^ Throttle is closed.
^ Engine coolant temperature is greater than 70°C (150°F).
^ Vehicle is in top gear.
^ No EGR pintle, TP Sensor, MAP, VSS, IAT, ECT or IAC DTCs have been set.
IMPORTANT: The EGR flow insufficient test is checked once per ignition cycle during deceleration.
DIAGNOSTIC AIDS
The Scan tool can read the number of deceleration test that have been performed since the DTCs were cleared. The Scan tool also displays the EGR decel average value as well as the FAIL threshold when the DTC will set. The average must be greater than the threshold to set P0401.
^ Carbon buildup around the EGR pintle valve bore opening may restrict exhaust gas flow. Build-up of carbon in the EGR passages will result in P0401.
^ Diagnose the other DTCs listed under parameters, especially a MAP sensor DTC before diagnosing P0401.
scientia non olet · About LEMON Manuals
Senior Member
Joined: Jan 2024
Posts: 641
From: Davison, MI
HERE'S THE TREE FOR THE P0405 CODE.
GOOD LUCK.
LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Saturn >> 1999 >> SL L4-1.9L SOHC VIN 8 >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0405
April 5, 2026: LEMON Manuals is launched! Read the announcement.
The linear EGR system consists of a linear EGR valve, the PCM and its associated wiring. The EGR valve solenoid is controlled directly by the PCM when certain conditions have been met. The PCM contains a diode feedback circuit which dissipates energy when the valve is cycled Off. When the PCM grounds the valve, a diagnostic feedback signal can determine if the valve had actually moved. DTC P0405 has been defined to monitor the feedback signal. This diagnostic will determine if the position feedback signal properly falls within the correct range under different valve operating conditions.
DTC PARAMETERS
DTC P0405 will set if the following condition are met:
^ IGN voltage is above 11.0 volts.
^ Voltage is less than 0.20 volts.
^ Condition present for greater than five seconds.
When this DTC fails, EGR will be disabled for the entire ignition cycle. The malfunction history record will aid in diagnosis.
IMPORTANT: The EGR valve may operate at any engine coolant temperature regardless of loop mode.
TEST DESCRIPTION
1. Normal closed valve position feedback voltage should be greater than 0.20 volts at all times.
2. A voltage of less than 0.2 volts indicates a problem with the position feedback circuit.
DIAGNOSTIC AIDS
^ Check for backed out or damaged electrical terminals.
^ Check the tightness of the female terminal grip with a spare male terminal.
^ A short to ground in the 5-volt reference will set both a P1635 and a P040 5. If both are set, diagnose P1635 first.
^ An open in the 5-volt reference will set only the P0405.
^ An open in the PCM diode feedback circuit will result in unstable valve operation resulting in vehicle surge.
scientia non olet · About LEMON Manuals
GOOD LUCK.
LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Saturn >> 1999 >> SL L4-1.9L SOHC VIN 8 >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0405
April 5, 2026: LEMON Manuals is launched! Read the announcement.
P0405
Diagnostic Chart:
Wiring Diagram:
The linear EGR system consists of a linear EGR valve, the PCM and its associated wiring. The EGR valve solenoid is controlled directly by the PCM when certain conditions have been met. The PCM contains a diode feedback circuit which dissipates energy when the valve is cycled Off. When the PCM grounds the valve, a diagnostic feedback signal can determine if the valve had actually moved. DTC P0405 has been defined to monitor the feedback signal. This diagnostic will determine if the position feedback signal properly falls within the correct range under different valve operating conditions.
DTC PARAMETERS
DTC P0405 will set if the following condition are met:
^ IGN voltage is above 11.0 volts.
^ Voltage is less than 0.20 volts.
^ Condition present for greater than five seconds.
When this DTC fails, EGR will be disabled for the entire ignition cycle. The malfunction history record will aid in diagnosis.
IMPORTANT: The EGR valve may operate at any engine coolant temperature regardless of loop mode.
TEST DESCRIPTION
1. Normal closed valve position feedback voltage should be greater than 0.20 volts at all times.
2. A voltage of less than 0.2 volts indicates a problem with the position feedback circuit.
DIAGNOSTIC AIDS
^ Check for backed out or damaged electrical terminals.
^ Check the tightness of the female terminal grip with a spare male terminal.
^ A short to ground in the 5-volt reference will set both a P1635 and a P040 5. If both are set, diagnose P1635 first.
^ An open in the 5-volt reference will set only the P0405.
^ An open in the PCM diode feedback circuit will result in unstable valve operation resulting in vehicle surge.
scientia non olet · About LEMON Manuals
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