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• | 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+ | B1370 04, B1380 04 | B1370 04, B1380 04 | -- | -- |
5 V REF | -- | 1 | -- | -- |
Ignition Terminal 1 | B1370 04, B1380 04 | B1370 04, B1380 04 | B1370 01 | -- |
Ignition Terminal 3 | B1370 04, B1380 04 | B1380 04 | B1380 01 | -- |
Signal Terminal 4 | B1370 04, B1380 04, B1441 04 | B1441 04 | B1441 01 | -- |
1. Power Mode Mismatch |
The vehicle power mode master is the body control module (BCM). The ignition switch is a low current switch with multiple discrete circuits to the BCM. The BCM logic uses the ignition switch positions to identify the operator's desired power mode and activate specific discrete signals, and serial data messages for the operation of different subsystems as necessary. Other modules which have switched voltage inputs may operate in a default mode if the power mode master serial data message does not match what the individual module can detect from its own connections.
The power mode master will activate relays and other direct outputs of the power mode master as needed according to the calculated power mode. Some relays controlled by the BCM are switched ignition voltage outputs that are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the B+ circuit fuse to the ignition switch will open.
Ignition switch is in the RUN or CRANK positions.
Ignition switch is in the RUN or ACCESSORY positions.
Ignition switch is in the CRANK position.
Ignition circuit is shorted to voltage.
• | Ignition circuit is open. |
• | Ignition, accessory, or off/run/crank circuit shorted to ground. |
• | B+ circuit of the ignition switch is open or shorted to ground. |
• | Ignition relay control circuit open, including relay coil and ground. |
Accessory circuit is shorted to voltage.
• | Accessory circuit is open. |
• | Ignition, accessory, or off/run/crank circuit shorted to ground. |
• | B+ circuit of the ignition switch is open or shorted to ground. |
Off/run/crank signal circuit is shorted to voltage.
Off/run/crank signal circuit is open.
• | The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the serial data communications circuits. |
• | The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the serial data communications circuits. |
• | The condition responsible for setting the DTC no longer exists. |
• | A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred. |
Power Mode Description and Operation
Control Module References for scan tool information
With a scan tool, access Power Mode data display list and compare all parameters listed with the corresponding ignition key position. The Power Mode Parameters table below illustrates the correct state of these input parameters in correspondence to the S39 ignition switch position. The circuits which the individual parameters are related to are in parentheses.
Ignition Switch Position | 5 V IGN (Ignition Switch, Terminal 4 and 6) | Accessory (Ignition Switch, Terminal 3) | Run/Crank (Ignition Switch, Terminal 1) |
---|---|---|---|
Off Key Out | Key Out/ACC | Inactive | Inactive |
Off Key IN | Key In/Off | Inactive | Inactive |
Accessory | Key Out/ACC | Active | Inactive |
Run | Run | Active | Active |
Start | Crank Request | Inactive | Active |
⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the ignition circuits listed below for a short to ground. |
Note: To help isolate a short to ground, it may be necessary to disconnect modules that are connected to the following circuits: |
• | Terminal 1 |
• | Terminal 3 |
• | Terminal 4 |
• | Terminal 6 |
⇒ | If less than 4.8 V, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
⇒ | If greater than 5.2 V, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the BCM. |
⇒ | If greater than 4.2 V, test the ignition switch signal circuit terminal 4 for a short to voltage. If the circuit tests normal, replace the BCM. |
⇒ | If less than 3 V, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
• | Terminal 5 |
• | Terminal 6 |
• | Terminal 15 |
• | Terminal 22 |
⇒ | If the test lamp illuminates, test the ignition circuits for a short to voltage. If the circuit tests normal, replace the S39 ignition switch. |
⇒ | If the test lamp does not illuminate, test the ignition circuit for an open/high resistance. If the circuit tests normal, replace the S39 ignition switch. |
⇒ | If the test lamp does not illuminate, test the ignition circuit for an open/high resistance. If the circuit tests normal, replace the S39 ignition switch. |
⇒ | If not the specified value, replace the S39 ignition switch. |
S39 Ignition Switch Position | Terminals 1 and 2 | Terminals 2 and 3 | Terminals 2 and 4 | Terminals 2 and 6 | Terminals 4 and 6 |
---|---|---|---|---|---|
Off Key Out | Infinite | Infinite | Infinite | Infinite | Infinite |
Off Key IN | Infinite | Infinite | < 5.0 Ω | Infinite | Infinite |
Accessory | Infinite | < 5.0 Ω | Infinite | Infinite | Infinite |
Run | < 5.0 Ω | < 5.0 Ω | Infinite | Infinite | < 5.0 Ω |
Start | < 5.0 Ω | Infinite | Infinite | Infinite | 1275-1325 Ω |
Perform the Diagnostic Repair Verification after completing the repair.
• | Control Module References for BCM replacement, setup, and programming |
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