PRE-RELEASE
DTC P0685 or P0686 (LLU)
| DTC P0685 or P0686 (LLU) |
| Diagnostic Instructions |
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Perform the
Diagnostic System Check - Vehicle
prior to using this diagnostic procedure.
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Review
Strategy Based Diagnosis
for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions
provides an overview of each diagnostic category.
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| DTC Descriptors |
DTC P0685 00
Engine Controls Ignition Relay Control Circuit
DTC P0686 00
Engine Controls Ignition Relay Control Circuit Low Voltage
| Diagnostic Fault Information |
| Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
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Coil Supply Voltage
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P0685 00
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P0685 00
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-
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-
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Control Circuit
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P0686 00
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P0685 00
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-
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P0685 00
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Signal Feedback Circuit
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P0686 00
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P0685 00, P0686 00
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P0685 00
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-
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| Typical Scan Tool Data |
Engine management system's ignition relay feedback signal
| Circuit | Normal Range | Short to Ground/Open | Short to Voltage |
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Operating Conditions:
Ignition ON, with the engine OFF
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Coil Supply Voltage
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-
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0 V
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B+
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Armature Supply Voltage
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-
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0 V
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-
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Control Circuit
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-
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0 V
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-
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Signal Feedback Circuit
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11-18 V
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0 V
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11-18 V
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| Circuit/System Description |
The powertrain relay is a normally open relay. The relay switch is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the relay switch contact at all times. The engine control module (ECM) supplies the ground path to the relay coil control circuit through an output driver module. The output driver module for the relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the relay ON, ignition voltage is supplied to fuses in the underhood fuse block.
The ignition voltage supplied to the ECM provides power to the internal ECM circuits associated with the throttle actuator control (TAC) operation. The ECM also monitors the voltage level on the ignition voltage circuit to confirm that the powertrain relay contacts have closed.
| Conditions for Running the DTC |
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The ignition is ON or the engine is running.
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The ignition voltage is between 8-16 V.
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These DTCs run continuously once the above conditions are met.
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| Conditions for Setting the DTC |
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The commanded state of the output driver module and the actual state of the control circuit do not match.
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The ECM detects that the feedback voltage is not within a predicted range when the relay is commanded ON and OFF.
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Either condition is present for more than 2 s.
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| Action Taken When the DTC Sets |
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DTCs P0685 00, and P0686 00 are Type D DTCs.
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Depending on the condition, the engine may not start.
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| Conditions for Clearing the DTC |
DTCs P0685 00, and P0686 00 are Type D DTCs.
| Diagnostic Aids |
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This test procedure assumes that the vehicle battery has passed a load test and is completely charged. Refer to
Battery Inspection/Test
.
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When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect the component electrical terminals for corrosion and the mating electrical terminals for correct tension.
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| Reference Information |
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
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Circuit Testing
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Connector Repairs
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Testing for Intermittent Conditions and Poor Connections
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Wiring Repairs
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DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
| Circuit/System Verification |
| Note | ||
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If you were sent here from engine cranks but does not run proceed to circuit/system testing. |
| 1. |
Ignition OFF, allow the ECM to completely power down. Probe both test points of F9, F10, and F11 fuses supplied with voltage by the KR75 Powertrain Relay. The test lamp should not illuminate on any test point of any fuse.
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| 2. |
Ignition ON, probe both test points of F9, F10, and F11 fuses supplied with voltage by the KR75 Powertrain Relay. The test lamp should illuminate on at lease one test point of each fuse.
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| 3. |
Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.
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| Circuit/System Testing |
| 1. |
Ignition OFF, disconnect the KR75 Powertrain Relay.
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| 2. |
Ignition ON, verify that a test lamp illuminates between the KR75 Powertrain Relay coil B+ socket circuit terminal 2 or 85 and ground.
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| 3. |
If the test lamp does not illuminate, repair the KR75 Powertrain Relay coil B+ circuit for a short to ground or an open/high resistance.
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| 4. |
Ignition OFF, connect a test lamp between the KR75 Powertrain Relay coil control socket circuit terminal 1 or 86 and the relay coil B+ socket circuit terminal 2 or 85.
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| 5. |
If the test lamp is always ON, test the KR75 Powertrain Relay coil control circuit for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module.
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| 6. |
Ignition ON. The test lamp should turn ON.
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| 7. |
If the test lamp is always OFF, test the KR75 Powertrain Relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.
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| 8. |
Install a 15 A fused jumper wire between the KR75 Powertrain Relay switch B+ socket circuit terminal 3 or 30 and the KR75 Powertrain Relay switch ignition voltage socket circuit terminal 5 or 87. |
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| 9. |
Attempt to start the engine. The engine should start.
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| 10. |
If the engine does not start, test the KR75 Powertrain Relay switch ignition voltage circuit between the KR75 Powertrain Relay circuit terminal 5 or 87 and the ECM connector X2 terminals 3 and 5 for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 engine control module.
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| 11. |
If all circuits test normal, test or replace the KR75 Powertrain Relay.
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| Component Testing |
Relay Test
| 1. |
Ignition OFF, disconnect the KR75 Powertrain Relay.
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| 2. |
Measure for 70-110 Ω between terminals 2 or 85 and 1 or 86 of the KR75 Powertrain Relay.
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| 3. |
If the resistance is not within the specified range, replace the KR75 Powertrain Relay.
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| 4. |
Measure for infinite resistance between following terminals of the KR75 Powertrain Relay:
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Terminals 3 or 30 and 1 or 86
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Terminals 3 or 30 and 5 or 87
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Terminals 3 or 30 and 2 or 85
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Terminals 2 or 85 and 5 or 87
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If continuity is detected, replace the KR75 Powertrain Relay.
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| 5. |
Connect a 20 A fused jumper wire from the positive terminal of the battery to KR75 Powertrain Relay terminal 2 or 85. Connect a jumper wire from the negative terminal of the battery to KR75 Powertrain Relay terminal 1 or 86. Measure for less than 5 Ω between KR75 Powertrain Relay terminal 3 or 30 and KR75 Powertrain Relay socket terminal 5 or 87.
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| 6. |
If the resistance measures more than 5 Ω, replace the KR75 Powertrain Relay.
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| Repair Instructions |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
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Relay Replacement (Attached to Wire Harness)
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Control Module References
for Engine Control Module replacement, setup, and programming
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