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Diagnostic Trouble Codes – P0401, P0402, P0403, P0404, P0405, P0406

Description

P0401 – EGR Flow Insufficient Detected

P0402 – EGR Flow Excessive Detected

P0403 – EGR Control Circuits

P0404 – EGR Control Circuit Range/Performance

P0405 – EGR Sensor A Circuit Low

P0406 – EGR Sensor A Circuit High

The Exhaust Gas Recirculation (EGR) system’s purpose is to redirect exhaust gas back into the cylinders. Since exhaust gas is inert (it won’t burn), it displaces oxygen and fuel, thereby lowering cylinder temperatures, 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.)

Test Procedure

(This example diagnosis is from a 2005 6.0 Ford F-250.)

Step 1:  Complete a visual inspection, retrieve/record any continuous and on-demand DTCs, and then record the freeze frame data. Clear all DTCs, and run a self-test again. Do any of the DTCs come back?

Yes–> For DTC P0401 or P0402, go to Step 2. For DTC P0403, go to Step 4. For DTC P0404 or P1335, go to Step 9. For DTC P0405, go to Step 10. For DTC P0406, go to Step 14.

No–>¬†Unable to duplicate the condition. Check for a loose connection and damaged or corroded terminals. Wiggle the harness to attempt to recreate the fault. Repair as necessary. If you need help with diagnosis, call a Hot Shot’s Secrets diesel expert at 1-800-341-6516 (toll free).

Step 2: Are there any other DTCs present?

Yes–> Address and correct them first.

No–> Go to Step 3.

Step 3: Access the EP, EGRVPDES, EGRDC, and EGRVP PIDs. Record the PID values. Key ON, engine running. Access Output State Control for the EGR valve. Monitor the EP PID while increasing and decreasing the EGRDC. Does EP reading indicate any EGR valve movement?

Yes–> Clear the DTCs and repeat the self-test.

No–> Replace the EGR valve and repeat the self-test.

Step 4: Key ON, engine OFF. Measure the voltage between EGR actuator connector pin E, harness side and ground. Is the voltage greater than 11.0 V?

Yes–> Go to Step 5.

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 5: Check the EGR actuator circuit for a short to voltage. Key OFF. Disconnect the PCM engine connector. Key on, engine off. Measure the voltage between the EGR actuator pin A, harness side and ground. Is the voltage less than 0.2 V?

Yes–> Go to Step 6.

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 6: Check the EGR actuator circuit for a short to ground. Key OFF. Measure the resistance between the EGR actuator pin A, harness side and ground. Is the resistance greater than 10,000 ohms?

Yes–> Go to Step 7.

No–> Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 7: Check the EGR control circuit for an open. Measure the resistance between the EGR actuator pin A, harness side and the PCM engine connector pin 23, harness side. Is the resistance less than 5 ohms?

Yes–> Go to Step 8.

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 8: Check the EGR actuator. Measure the resistance between the EGR actuator pin A, component side and the EGR actuator pin E, component side. Is the resistance between 4 and 10 ohms?

Yes–>¬†Install a new PCM. Clear the DTCs. Repeat the self-test.

No–> Install a new EGR actuator. Repeat the self-test.

Step 9: Are there any other codes present?

Yes–> Address other codes first.

No–>¬†Carry out the Exhaust Gas Recirculation (EGR) position test. For more information, call a Hot Shot’s Secret diesel expert at 1-800-341-6516 (toll free).

Step 10: Key OFF. Disconnect the EGR actuator. Key ON, engine OFF. Measure the voltage between EGR actuator pin D, harness side and the EGR actuator pin B, harness side. Is the voltage between 4.5 and 5.5 V?

Yes–> ¬†Go to Step 11.

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 11: Check EGR position signal circuit for a short to ground. Key OFF. Disconnect the PCM engine connector. Measure the resistance between the EGR actuator pin C, harness side and ground. Is the resistance greater than 10,000 ohms?

Yes–> Go to Step 12.

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 12: Check the EGR position signal circuit for an open. Measure the resistance between the PCM engine connector pin 33, harness side and the EGR actuator pin C, harness side. Is the resistance less than 5 ohms?

Yes–> Go to Step 13

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 13: Check the EGR actuator. Measure the resistance between the EGR actuator pins, component side as follows:

  • Pins B and C: 50-2,500 ohms
  • Pins C and D: 2,000-7,000 ohms
  • Pins B and D: 3,000-7,000 ohms

Are the resistances within specifications? 

Yes–> Install a new PCM, clear DTCs and repeat the self test

No–> Install new EGR actuator, clear the DTCs and repeat the self test

Step 14: Key OFF. Disconnect the EGR actuator. Key ON, engine OFF. Carry out the on-demand self-test. Is DTC P0405 present?

Yes–> Install new EGR actuator. Clear codes, and run self test.

No–> Go to step 15

Step 15: Check the EGR position signal circuit for a short to voltage. Key OFF. Disconnect the PCM engine harness connector. Key ON, engine OFF. Measure the voltage between the EGR actuator pin C, harness side and ground. Is the voltage less than 0.2 volts?

Yes–> Go to Step 16

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

Step 16: Check the signal return circuit for an open. Key OFF. Measure the resistance between EGR actuator pin B, harness side and the PCM engine connector pin 25, harness side. Is the resistance less than 5 ohms?

Yes–> Install a new PCM. Clear codes and run self test.

No–>¬†Repair the circuit. Clear the DTCs. Repeat the self-test.

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