• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
Underhood Fuse Block B+ | 1 | 1 | -- | -- |
175 A MEGA Fuse | -- | 1 | -- | -- |
ECM-IGN Fuse 56 (LMM) or 58 (w/o LMM) | -- | 1 | -- | -- |
STRTR Fuse 60 (LMM) or 64 (w/o LMM) | -- | 1 | -- | -- |
ECM Ignition 1 Voltage | 1 | 1 | -- | -- |
Park Neutral Signal | 2 | 1 | 1 | -- |
Starter Relay Coil Control | 1 | 1 | 3 | -- |
Starter Solenoid Crank Voltage | 1 | 1 | 3 | -- |
Underhood Fuse Block Ground | -- | 1 | -- | -- |
|
The engine control module (ECM) controls engine cranking based on a power mode input and the status of the park/neutral position (PNP) switch. With the transmission in Park/Neutral, voltage at the ECM PNP switch signal circuit is low. This indicates to the ECM that conditions are acceptable for cranking. When a power mode crank request is seen, the ECM applies voltage to the starter relay coil control circuit. This energizes the coil side of the relay, which pulls the switch side of the relay closed, applying voltage to the starter X2-S terminal and engaging the starter solenoid.
• | Automatic Transmission Controls Schematics (M30 4L60E, M70 4L70E) |
• | Automatic Transmission Controls Schematics (MYC 6L80E) |
• | Automatic Transmission Controls Schematics (MW7 Allison) |
Starting and Charging Schematics
Engine Electrical Connector End Views
Starting System Description and Operation
• | Inspect the STRTR Fuse 60 (LMM Diesel) or 64 (w/o LMM), ECM-IGN Fuse 56 (LMM) or 58 (w/o LMM), and the 175 A MEGA Fuse for an open. |
• | A misadjusted PNP switch (M30 4L60E, M70 4L70E) or range selector lever cable may result in a starter solenoid does not click condition. |
⇒ | If less than the specified value, test the Run/Crank relay, ECM-IGN fuse, and the ECM ignition 1 circuits for an open. |
⇒ | If the scan tool PNP Switch parameter is not Park/Neutral, refer to Circuit/System Testing: PNP Switch Circuit Malfunction. |
⇒ | If the solenoid does not engage, refer to Circuit/System Testing: STRTR Relay Circuit Malfunction. |
⇒ | If the solenoid engages but the engine does not crank, refer to Starter Solenoid Clicks, Engine Does Not Crank . |
⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance. |
⇒ | If not the specified value, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the ECM. |
⇒ | If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
⇒ | 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. |
⇒ | If not the specified value, replace the ECM. |
⇒ | If not the specified value, replace the ECM. |
⇒ | If not the specified value, test the signal circuit terminal R for a short to ground. If the circuit tests normal, replace the ECM. |
⇒ | If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance. |
⇒ | 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. |
Important: The engine may begin to crank.
⇒ | 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. |
Important: The engine may begin to crank.
⇒ | 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. |
• | R |
• | OD |
• | D |
• | 2 |
• | 1 |
⇒ | If not the specified value, replace the PNP switch. |
• | P |
• | N |
⇒ | If greater than the specified range, replace the PNP switch. |
⇒ | If not within the specified range, replace the relay. |
• | 30 and 86 |
• | 30 and 87 |
• | 30 and 85 |
• | 85 and 87 |
⇒ | If not the specified value, replace the relay. |
⇒ | If greater than specified range, replace the relay. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Range Selector Lever Cable Adjustment (M30 4L60E, M70 4L70E) |
• | Range Selector Lever Cable Adjustment (MYC 6L80E) |
• | Range Selector Lever Cable Adjustment (MW7 Allison) |
• | Park/Neutral Position Switch Adjustment (M30 4L60E, M70 4L70E) |
• | Park/Neutral Position Switch Replacement (M30 4L60E, M70 4L70E) |
• | Control Valve Body Assembly Removal for shift shaft position switch replacement (MYC 6L80E) |
• | Control Valve Body Assembly Disassemble for shift shaft position switch replacement (MYC 6L80E) |
• | Transmission Internal Mode Switch Replacement (MW7 Allison) |
• | Starter Motor Solenoid Replacement 6.6L Diesel (LMM) |
• | Control Module References for BCM or ECM replacement, setup and programming. |