• | 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 |
---|---|---|---|---|
B+ terminal 30 | 1 | 1 | -- | -- |
ECM Park/ Neutral Signal | 2 | 1 | -- | -- |
Coil Control terminal 86 | -- | 1 | 3 | -- |
Control Output terminal 87 | 1 | 1 | 3 | -- |
Coil Ground terminal 85 | -- | 1 | -- | -- |
1. No crank 2. Cranks in any gear 3. Cranks all the time |
When the ignition switch is placed in the START position, a discrete signal is supplied to the body control module (BCM) notifying it that the ignition is in the START position. The BCM then sends a message to the engine control module (ECM) that crank has been requested. The ECM then verifies that the transmission is in Park/Neutral. If it is, the ECM then supplies 12 V to the control circuit of the crank relay. When this occurs, battery voltage is supplied through the switch of the crank relay to the starter solenoid.
• | Automatic Transmission Controls Schematics for the 4L60/4L65/4L70-E transmission. |
• | Automatic Transmission Controls Schematics for the 4L80/4L85-E transmission. |
Starting System Description and Operation
Control Module References for scan tool information
⇒ | If DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle. |
⇒ | If not the specified value, refer to Power Mode Mismatch. |
⇒ | If the TCM parameter does not indicate Park/Neutral. Refer to Range Selector Displays Incorrect Range for the 4L60/4L65/4L70-E transmission. or Range Selector Displays Incorrect Range for the 4L80/4L85-E transmission. |
⇒ | If the ECM Park/Neutral parameter does not indicate Park/Neutral. Refer to ECM Park Switch Circuit Malfunction. |
⇒ | If the crank relay does not click or the engine does not crank, refer to Crank Relay Circuit Malfunction. |
⇒ | If not the specified value, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
⇒ | If greater than the specified range, 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. |
⇒ | If the solenoid does not engage, test the control output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the starter motor. |
⇒ | If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
⇒ | If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Transmission Internal Mode Switch Logic for the 4L60/4L65/4L70-E transmission |
• | Park/Neutral Position Switch Replacement for the 4L80/4L85-E transmission. |
• | Control Module References for ECM replacement, setup and programming |