1996 Chevrolet Blazer - 4WD 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 Action Value(s) Yes No Important 1 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? Go to Step 2 Go to Powertrain On Board Diagnostic (OBD) System Check 2 1. Turn the ignition switch ON, with the engine 2. Connect the scan tool. 3. Monitor the Actual EGR Pintle Position. 0% Does the scan tool display the specified value? 1. Turn the ignition switch ON, with the engine Go to Step 3 Go to Step 9
3 2. Command the EGR Valve through the specified values. Does the Actual EGR Position follow the Commanded Position? 20%, 50%, 70%,100% Go to Diagnostic Aids Go to Step 4 4 1. Turn the ignition switch ON, with the engine 2. Command the EGR Valve to the specified value. 30% Does the Actual EGR Position fluctuate severely? Go to Step 34 Go to Step 5 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. 100% Go to Step 23 Go to Step 6 6 1. Connect a test light to a known good ground. 2. Probe the EGR Valve harness connector terminal E. Go to Step 7 Go to Step 13 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. Go to Step 8 Go to Step 36 8 Repair the faulty connections or open in the EGR Valve Control circuit as necessary. Refer to Wiring Repairs in Electrical 9 10 11 12 Is DTC P0108 also set? Disconnect the EGR Valve electrical connector. 0% Is the Actual EGR Valve Position at the specified value? Check for a short to voltage in the EGR Pintle Position circuit. Repair short to voltage in the EGR Pintle Position Go to Step 38 Go to DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage Go to Step 10 Go to Step 17 Go to Step 11 Go to Step 12 Go to Step 36
13 14 15 Go to Step 38 Check for a blown EGR Ignition Feed fuse. Was the EGR Ignition Feed fuse blown? Replace EGR Ignition Feed fuse. Repair the short to ground in the EGR Ignition Feed Go to Step 14 Go to Step 16 Go to Step 15 16 17 18 19 20 21 22 23 Repair the open EGR Ignition Feed circuit. Refer to Wiring Repairs in Electrical 1. Connect a test light to B+. 2. Probe the EGR valve harness connector terminal B. 1. Connect a test light to B+. 2. Probe the EGR valve harness connector terminal A. 1. Turn the ignition switch 2. Disconnect the Blue VCM connector. 3. Turn the ignition switch ON, with engine 4. Connect a test light to B+. 5. Probe the EGR valve harness connector terminal A. Repair short to ground in the EGR Valve Control Check for a faulty connection at the EGR valve harness connector. Repair the faulty connection at the EGR valve harness connector. Refer to Wiring Repairs in Electrical Connect a DMM J 39200 between the EGR Valve connector terminals B and D. 5.0V Go to Step 38 Go to Step 38 Go to Step 18 Go to Step 25 Go to Step 19 Go to Step 21 Go to Step 20 Go to Step 36 Go to Step 38 Go to Step 22 Go to Step 33 Go to Step 38
24 25 Is the voltage near the specified value? Go to Step 27 Go to 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? Check for open in EGR Sensor Ground circuit and repair as necessary. Refer to Wiring Repairs in Electrical 5.0V Go to Step 25 Go to Step 26 26 27 28 29 30 31 32 33 Was repair necessary? Check for open in EGR 5 Volt reference circuit and repair as necessary. Refer to Wiring Repairs in Electrical Was a repair necessary? 1. Connect a test light to B+. 2. Probe the EGR valve harness connector terminal C. Check for a short to ground in the EGR Pintle Position circuit. Repair the short to ground in the EGR Pintle Position 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? 1. Check for open in the EGR Pintle Position circuit. 2. Check for a poor connection at the EGR Valve connector. Repair the open or poor connection in the EGR pintle position circuit. Refer to Wiring Repairs in Electrical Replace the EGR valve. Refer to EGR Valve Replacement in Repair Instructions. 1. Turn the ignition switch 2. Disconnect the C1 (Blue) VCM connector. 100% Go to Step 38 Go to Step 36 Go to Step 38 Go to Step 36 Go to Step 28 Go to Step 30 Go to Step 29 Go to Step 36 Go to Step 38 Go to Step 33 Go to Step 31 Go to Step 32 Go to Step 36 Go to Step 38 Go to Step 38
34 3. Turn the ignition switch ON, with the engine 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. Go to Step 36 Go to Step 35 35 Repair open in ignition feed circuit to Pin 4 of the C1 (Blue) VCM connector. Refer to Wiring Repairs in Electrical Go to Step 38 36 Check for poor connections at the VCM harness connectors and repair as necessary. Refer to Wiring Repairs in Electrical Was a repair necessary? Go to Step 38 Go to Step 37 Important 37 Program the new VCM. Refer to VCM Replacement/Programming in Repair Instructions. Replace the VCM. Go to Step 38 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? Go to Step 39 Go to Step 2 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? Go to the applicable DTC table System OK