Chevrolet Silverado / GMC Sierra. Manual

If the solenoid engages but the engine does not crank, refer to Starter Solenoid
Clicks, Engine Does Not Crank.

Circuit/System Testing

PNP Switch Circuit Malfunction (M30 4L60E, M70 4L70E)

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector

Lever Cable Adjustment .

2. Inspect the park/neutral position switch for proper adjustment. Refer to Park/Neutral

Position Switch Adjustment .

3. Ignition OFF. Disconnect the harness connector from the park/neutral switch. Refer to

Park/Neutral Position Switch Replacement .

4. Ignition ON. Probe the ground circuit terminal 7 with a test lamp that is connected to B+.

Verify that the test lamp illuminates.

If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

5. Verify that the scan tool PNP Switch parameter is In Gear.

If not the specified value, test the signal circuit terminal 3 for a short to ground. If the
circuit tests normal, replace the ECM.

6. Install a 3 A fused jumper wire between the ground circuit terminal 7 and the signal circuit

terminal 3. Verify that the scan tool PNP Switch parameter is Park/Neutral.

If not the specified value, test the signal circuit for an open/high resistance. If the
circuit tests normal, replace the ECM.

7. If all circuits test normal, test or replace the park/neutral position switch.

PNP Switch Circuit Malfunction (MYC 6L80E, MYD 6L90E)

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector

Lever Cable Adjustment .

2. Ignition OFF. Disconnect the 16-way harness connector from the transmission.

3. Ignition ON. Measure voltage on the park/neutral signal circuit terminal 3 with a DMM.

Verify that there is greater than 10 volts on the park/neutral signal circuit.

If there is less than 10 volts on the park/neutral signal circuit, test the circuit for an
open or a short to ground. If OK, replace the ECM.

4. Ignition OFF, reconnect the 16-way harness connector to the transmission.

5. Remove the automatic transmission fluid pan. Refer to Automatic Transmission Fluid,

Fluid Pan and/or Filter Replacement .

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

6. Disconnect the manual shift shaft position switch connector at the control solenoid valve

assembly. Refer to Manual Shift Shaft Position Switch Replacement .

7. Ignition ON, verify that the scan tool PNP Switch parameter displays In Gear.

If not the specified value, replace the ECM.

8. Connect a 3-amp fused jumper wire between the park/neutral signal terminal F at the

control solenoid valve assembly and ground. The scan tool PNP Switch parameter should
display Park/Neutral when the terminal is connected to ground.

If not the specified value, replace the ECM.

9. If all components test normal, test or replace the manual shift shaft position switch.

PNP Switch Circuit Malfunction (MW7 Allison)

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector

Lever Cable Adjustment .

2. Ignition OFF. Disconnect the engine chassis harness to transmission internal harness

connector X175.

3. Verify that the scan tool PNP Switch parameter is In Gear.

If not the specified value, test the signal circuit terminal R for a short to ground. If the
circuit tests normal, replace the ECM.

4. Install a 3A fused jumper wire between the signal circuit terminal R and ground. Verify that

the scan tool PNP Switch parameter is Park/Neutral.

If not the specified value, test the signal circuit for an open/high resistance. If the
circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the transmission internal mode switch.

STRTR Relay Circuit Malfunction

1. Ignition OFF, disconnect the STRTR relay.

2. Ignition ON, transmission in Park/Neutral. Verify that a test lamp illuminates between the

relay coil ground circuit terminal and B+.

If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Probe the STRTR Relay switch B+ circuit terminal with a test lamp that is connected to

ground. Verify that the test lamp illuminates.

If the test lamp does not illuminate, test the B+ circuit for a short to ground or an
open/high resistance. Inspect the 175 A MEGA fuse for an open. If the circuit tests
normal and the 175 A MEGA fuse is open, test the relay controlled output circuit for a
short to ground.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

4. Connect a test lamp between the relay coil ground circuit terminal and the relay coil control

circuit terminal.

5. Ignition ON, transmission in Park/Neutral. Command the Starter Relay ON and OFF with a

scan tool, or turn the ignition switch between the START and RUN positions. The test lamp
should turn ON and OFF when changing between the commanded states.

If the test lamp is always ON, test the relay coil control circuit for a short to voltage. If
the circuit tests normal, replace the ECM.

If the test lamp is always OFF, test the relay coil control circuit for a short to ground
or and open/high resistance. Inspect the STRTR fuse for an open. If the STRTR fuse is
open, test the relay controlled output circuit for a short to ground, or replace the
starter solenoid (LMM) or starter. If the circuit and fuse test normal, replace the ECM.

6. Connect the STRTR relay.

7. Install a test lamp between the starter X2-S terminal and ground.

8. Ignition ON, transmission in Park/Neutral, command the Starter Relay ON with a scan tool,

or turn the ignition switch to the START position. The test lamp should illuminate.

If the test lamp does not illuminate, test the relay controlled output circuit for an
open/high resistance. If the circuit tests normal, test or replace the STRTR relay.

9. If all circuits test normal, test or replace the starter, or the starter solenoid (LMM 6.6L

Diesel).

Component Testing

PNP Switch (M30 4L60E, M70 4L70E)

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector

Lever Cable Adjustment .

2. Inspect the park/neutral position switch for proper adjustment. Refer to Park/Neutral

Position Switch Adjustment .

3. Ignition OFF. Disconnect the harness connector from the park/neutral switch. Refer to

Park/Neutral Position Switch Replacement .

4. With the PNP switch in the following positions, test for infinite resistance between the

ground terminal 7 and the signal terminal 3.

IMPORTANT: The engine may begin to crank.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

If not the specified value, replace the PNP switch.

5. With the PNP switch in the following positions, test for less than 2.0 ohms between the

ground terminal 7 and the signal terminal 3.

If greater than the specified range, replace the PNP switch.

STRTR Relay

1. Ignition OFF, remove the STRTR relay. Refer to Relay Replacement (Attached to Wire

Harness) or Relay Replacement (Within an Electrical Center) .

2. Test for 60-180 ohms between terminals 85 and 86.

If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

30 and 86

30 and 87

30 and 85

85 and 87

If not the specified value, replace the relay.

4. Install a 20 amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper

wire between relay terminal 86 and ground. Test for less than 2.0 ohms between terminals
30 and 87.

If greater than specified range, replace the relay.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Clutch Pedal Position Sensor Learn (TZ0 Manual)

Range Selector Lever Cable Adjustment (M30 4L60E, M70 4L70E)

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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Chevrolet Silverado / GMC Sierra. Manual - part 1702