DTC P1491: EGR Valve Insufficient Lift

Reset the ECM/PCM (see HOW TO RESET THE ECM/PCM ).
Start the engine. Hold the engine at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on.
Check for a Temporary DTC with the scan tool.
Test-drive the vehicle for approx. 10 minutes. Try to keep the engine speed in the 1,700-2,500 RPM range.
Is Temporary DTC P1491 indicated?
1. YES -Go to step 5.
2. NO -Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the EGR valve and the ECM/PCM.
Turn the ignition switch OFF.
Disconnect the EGR valve 6P connector.
Start the engine and let it idle.
Measure voltage between EGR valve 6P connector terminals No. 4 and No. 6.

Fig 1: Measuring Voltage Between EGR Valve 6P Connector Terminals No. 4 & No. 6
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there battery voltage?
1. YES -Substitute a known-good ECM/PCM and recheck (see HOW TO SUBSTITUTE THE ECM/PCM FOR TESTING PURPOSES ). If the symptom/indication goes away, replace the original ECM/PCM.
2. NO -Go to step 9.
Turn the ignition switch OFF.
Turn the ignition switch ON (II).
Measure voltage between EGR valve 6P connector terminals No. 2 and No. 3.

Fig 2: Measuring Voltage Between EGR Valve 6P Connector Terminals No. 2 & No. 3
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there approx. 5 V?
1. YES -Go to step 13.
2. NO -Go to step 12.
Measure voltage between ECM/PCM connector terminals C18 and C28.

Fig 3: Measuring Voltage Between ECM/PCM Connector Terminals C18 & C28
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there approx. 5 V?
1. YES -Repair open in the wire between the EGR valve and the ECM/PCM (C18, C28).
2. NO -Substitute a known-good ECM/PCM and recheck (see HOW TO SUBSTITUTE THE ECM/PCM FOR TESTING PURPOSES ). If the symptom/indication goes away, replace the original ECM/PCM.
Turn the ignition switch OFF.
At the sensor side, measure resistance between EGR valve 6P connector terminals No. 1 and No. 2.

Fig 4: Measuring Resistance Between EGR Valve 6P Connector Terminals No. 1 & No. 2
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is the resistance 100 kΩ or more?
1. YES -Replace the EGR valve.
2. NO -Go to step 15.
Measure resistance between EGR valve 6P connector terminals No. 1 and No. 3.

Fig 5: Measuring Resistance Between EGR Valve 6P Connector Terminals No. 1 & No. 3
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there 100 kΩ or more?
1. YES -Replace the EGR valve.
2. NO -Go to step 16.
Reconnect the EGR valve connector.
Turn the ignition switch ON (II).
Measure voltage between ECM/PCM connector terminals C6 and C18.

Fig 6: Measuring Voltage Between ECM/PCM Connector Terminals C6 & C18
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there approx. 1.2 V?
1. YES -Go to step 19.
2. NO -Repair short in the wire between the EGR valve and the PCM (C8).
Turn the ignition switch OFF.
Connect EGR valve 6P connector terminal No. 1 to body ground with a jumper wire.

Fig 7: Connecting EGR Valve 6P Connector Terminal No. 1 To Body Ground With A Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Check for continuity between ECM/PCM connector terminal C6 and body ground.

Fig 8: Checking For Continuity Between ECM/PCM Connector Terminal C6 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES -Go to step 22.
2. NO -Repair open in the wire between the EGR valve and the ECM/PCM (C6).
Disconnect the EGR valve 6P connector.
Connect the battery positive terminal to EGR valve 6P connector terminal No. 4 with a jumper wire.

Fig 9: Connecting The Battery Positive Terminal To EGR Valve 6P Connector Terminal No. 4 With A Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Start the engine and let it idle, then connect the battery negative terminal to EGR valve 6P connector terminal No. 6 with a jumper wire.
Does the engine stall or run rough?
1. YES -Go to step 25.
2. NO -Replace the EGR valve.
Turn the ignition switch OFF.
Disconnect ECM/PCM connector B (25P).
Turn the ignition switch OFF.
Connect EGR valve 6P connector terminal No. 4 to body ground with a jumper wire.

Fig 10: Connecting EGR Valve 6P Connector Terminal No. 4 To Body Ground With A Jumper Wire
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Check for continuity between ECM/PCM connector terminal B7 and body ground.

Fig 11: Checking For Continuity Between ECM/PCM Connector Terminal B7 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES -Go to step 30.
2. NO -Repair open in the wire between the EGR valve and the ECM/PCM (B7).
Check for continuity between ECM/PCM connector terminal B7 and body ground.

Fig 12: Checking For Continuity Between ECM/PCM Connector Terminal B7 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES -Repair short in the wire between the EGR valve and the ECM/PCM (B7).
2. NO -Go to step 31.
Check for continuity between EGR valve 6P connector terminal No. 6 and body ground.

Fig 13: Checking For Continuity Between EGR Valve 6P Connector Terminal No. 6 & Body Ground
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Is there continuity?
1. YES -Substitute a known-good ECM/PCM and recheck (see HOW TO SUBSTITUTE THE ECM/PCM FOR TESTING PURPOSES ). If the symptom/indication goes away, replace the original ECM/PCM.
2. NO -Repair open in the wire between the EGR valve and G101.