Help!!! Service Engine Light

Robinhood · March 19, 2003

Wife's 96 Blazer (4.3 liter) has an intermittent service engine light now for a couple weeks. I had it scanned with a code of #1406 which is for the EGR position senser. Anyone know what is involved to rectify this or is a trip to the dealer in order?

CMNTMXR81 · March 19, 2003

Oh do I. That's a code I get all the time on my 96 Monte Carlo.

Here is the exact procedure from GM.

DTC P1406 Exhaust Gas Recirculation (EGR) Position Sensor Performance

Circuit Description

The VCM constantly monitors the linear EGR valve pintle position sensor in order to ensure that the valve is responding properly to the commands from the VCM. The DTC P1406 is a type A DTC.

Conditions for Setting the DTC

The following conditions will set the DTC:

- EGR pintle position signal indicates a voltage out of the normal range of the pintle position sensor, or a signal that is 10% greater or less than the VCM commanded position

- Ignition voltage greater than 9 volts

Action Taken When DTC Sets

If a current DTC P1406 sets during 2 consecutive test cycles, the VCM turns ON the MIL.

Conditions for Clearing the MIL/DTC

The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids

A poor connection or a rubbed-through wire insulation may cause an intermittent condition. Check for the following conditions:

- A poor connection or a damaged harness - Inspect VCM harness connectors for backed out terminals BLK 18, GRY 27, GRY19, or RED 10 for the following items:

- Improper mating

- Broken locks

- Improperly formed or damaged terminals

- A poor terminal to wire connection

- A damaged harness

Intermittent test - If the connections and the harness check OK, monitor a digital voltmeter connected between the affected terminals and the ground while moving the related connectors and the wiring harness. If the failure is induced, the voltage reading will change.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2) Checks for an EGR valve sticking partially open or an incorrect pintle position sensor feedback signal.

3) This step determines if this DTC was set during an intermittent condition. If the fault that set this DTC is not present, check for other stored DTCs.

5) Checks the EGR valve driver in the VCM and the EGR Control circuit.

6) This checks for EGR Valve Ignition Feed at the EGR valve.

38) Clearing the DTC Information is a very important step in this diagnostic. This allows the EGR Valve to relearn a new minimum pintle position.

Step 1

Important

Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear DTC Information function is used.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Yes: Go to Step 2

No: Go to Powertrain On Board Diagnostic (OBD) System Check

Step 2

1) Turn the ignition switch ON, with the engine OFF.

2) Connect the scan tool.

3) Monitor the Actual EGR Pintle Position.

Does the scan tool display the specified value?

Specified Value = 0%

--

Yes: Go to Step 3

No: Go to Step 9

Step 3

1) Turn the ignition switch ON, with the engine OFF.

2) Command the EGR Valve through the specified values.

Does the Actual EGR Position follow the Commanded Position?

Command Position = 20%, 50%, 70%,100%

--

Yes: Go to Diagnostic Aids

No: Go to Step 4

Step 4

1) Turn the ignition switch ON, with the engine OFF.

2) Command the EGR Valve to the specified value.

Does the Actual EGR Position fluctuate severely?

Severity of = 30%

--

Yes: Go to Step 34

No: Go to Step 5

Step 5

1) Disconnect the EGR Valve electrical connector.

2) Connect a test light between the EGR Valve harness connector terminals A and E.

3) Command the EGR Position to the specified value.

Is the test light ON?

light on 100%

--

Yes: Go to Step 23

No: Go to Step 6

Step 6

1) Connect a test light to a known good ground.

2) Probe the EGR Valve harness connector terminal E.

Is the test light ON?

--

Yes: Go to Step 7

No: Go to Step 13

Step 7

1) Check for a faulty connection at the EGR Valve harness connector terminal A.

2) Check for an open in the EGR Valve Control Circuit.

Was a problem found?

--

Yes: Go to Step 8

No: Go to Step 36

Step 8

Repair the faulty connections or open in the EGR Valve Control circuit as necessary. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 9

Is DTC P0108 also set?

--

Yes: Go to DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage

No: Go to Step 10

Step 10

Disconnect the EGR Valve electrical connector.

Is the Actual EGR Valve Position at the specified value?

Specified Value = 0%

--

Yes: Go to Step 17

No: Go to Step 11

Step 11

Check for a short to voltage in the EGR Pintle Position circuit.

Was a problem found?

--

Yes: Go to Step 12

No: Go to Step 36

Step 12

Repair short to voltage in the EGR Pintle Position circuit. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 13

Check for a blown EGR Ignition Feed fuse.

Was the EGR Ignition Feed fuse blown?

--

Yes: Go to Step 14

No: Go to Step 16

Step 14

Replace EGR Ignition Feed fuse.

Is the action complete?

--

Yes: Go to Step 15

--

Step 15

Repair the short to ground in the EGR Ignition Feed circuit. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 16

Repair the open EGR Ignition Feed circuit. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 17

1) Connect a test light to B+.

2) Probe the EGR valve harness connector terminal B.

Is the test light ON?

--

Yes: Go to Step 18

No: Go to Step 25

Step 18

1) Connect a test light to B+.

2) Probe the EGR valve harness connector terminal A.

Is the test light ON?

--

Yes: Go to Step 19

No: Go to Step 21

Step 19

1) Turn the ignition switch OFF.

2) Disconnect the Blue VCM connector.

3) Turn the ignition switch ON, with engine OFF.

4) Connect a test light to B+.

5) Probe the EGR valve harness connector terminal A.

Is the test light ON?

--

Yes: Go to Step 20

No: Go to Step 36

Step 20

Repair short to ground in the EGR Valve Control circuit. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 21

Check for a faulty connection at the EGR valve harness connector.

Was a problem found?

--

Yes: Go to Step 22

No: Go to Step 33

Step 22

Repair the faulty connection at the EGR valve harness connector. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 23

Connect a DMM J 39200 between the EGR Valve connector terminals B and D.

Is the voltage near the specified value?

Specified Value = 5.0V

--

Yes: Go to Step 27

No: Go to Step 24

Step 24

Connect a DMM J 39200 between the EGR harness connector terminal D and a known good ground.

Is the voltage at the specified value?

Specified Value = 5.0V

--

Yes: Go to Step 25

No: Go to Step 26

Step 25

Check for open in EGR Sensor Ground circuit and repair as necessary. Refer to Wiring Repairs in Electrical Diagnosis.

Was repair necessary?

--

Yes: Go to Step 38

No: Go to Step 36

Step 26

Check for open in EGR 5 Volt reference circuit and repair as necessary. Refer to Wiring Repairs in Electrical Diagnosis.

Was a repair necessary?

--

Yes: Go to Step 38

No: Go to Step 36

Step 27

1) Connect a test light to B+.

2) Probe the EGR valve harness connector terminal C.

Is the test light ON?

--

Yes: Go to Step 28

No: Go to Step 30

Step 28

Check for a short to ground in the EGR Pintle Position circuit.

Was a problem found?

--

Yes: Go to Step 29

No: Go to Step 36

Step 29

Repair the short to ground in the EGR Pintle Position circuit. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 30

Using proper test adapters from Connector Test Adapter kit J 35616-A , install a jumper between terminals D and C of the EGR harness connector.

Is the Actual EGR Position near the specified value?

Specified Value = 100%

--

Yes: Go to Step 33

No: Go to Step 31

Step 31

1) Check for open in the EGR Pintle Position circuit.

2) Check for a poor connection at the EGR Valve connector.

Was a problem found?

--

Yes: Go to Step 32

No: Go to Step 36

Step 32

Repair the open or poor connection in the EGR pintle position circuit . Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 33

Replace the EGR valve. Refer to EGR Valve Replacement in Repair Instructions.

Is the action complete?

--

Yes: Go to Step 38

--

Step 34

1) Turn the ignition switch OFF.

2) Disconnect the C1 (Blue) VCM connector.

3) Turn the ignition switch ON, with the engine OFF.

4) Connect a test light to a known good ground.

5) Probe Pin 4 of the C1 (Blue) VCM connector with proper test adapter from Connector Test Adapter kit J 35616-A .

Is the test light ON?

--

Yes: Go to Step 36

No: Go to Step 35

Step 35

Repair open in ignition feed circuit to Pin 4 of the C1 (Blue) VCM connector. Refer to Wiring Repairs in Electrical Diagnosis.

Is the action complete?

--

Yes: Go to Step 38

--

Step 36

Check for poor connections at the VCM harness connectors and repair as necessary. Refer to Wiring Repairs in Electrical Diagnosis.

Was a repair necessary?

--

Yes: Go to Step 38

No: Go to Step 37

Step 37

Important

Program the new VCM. Refer to VCM Replacement/Programming in Repair Instructions.

Replace the VCM.

Is the action complete?

--

Yes: Go to Step 38

--

Step 38

1) Use the scan tool, in order to select the DTC and the Clear DTC Information function.

2) Start the engine.

3) Allow the engine to idle until the normal operating temperature is reached.

4) Select the DTC and the Specific DTC functions.

5) Enter the DTC number which was set.

6) Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does scan tool indicate that this diagnostic ran and passed?

--

Yes: Go to Step 39

No: Go to Step 2

Step 39

Use the scan tool in order to display the Capture Info and the Review Capture Info functions.

Are there any DTCs displayed that have not been diagnosed?

--

Yes: Go to the applicable DTC table

No: System OK