P1594

DTC P1594

Circuit Description
The idle up volume controls the idle speed during warm-up and it is installed in the driver's side instrument panel. This volume is active only when the gear position is the neutral position (parking or neutral position for automatic transmission vehicle). When the shift lever is moved to another position, the volume is canceled. The engine control module (ECM) receives the idle up signal from the idle up volume and controls the fuel injection quantity. The idle up volume has following circuits.
- 5 volts reference circuit.
- Low reference circuit.
- Idle up volume signal circuit.

The ECM monitors the idle up volume signals for voltages outside the normal range of the idle up volume. If the ECM detects an excessively high idle up volume voltage, this DTC will set.

Condition for Running the DTC
- The battery voltage is between 10-16 volts.
- The ignition switch is ON.

Condition for Setting the DTC
- The ECM detects that the idle up volume signal voltage is more than 4.8 volts.

Action Taken When the DTC Sets
- The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
- The ECM disables idle up volume control.

Condition for Clearing the DTC
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
If an intermittent condition is suspected, the following may cause an intermittent:
- Poor connections.
- Misrouted harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation.

Check for the following conditions:
- Poor connection at ECM: Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness: Inspect the wiring harness for damage. If the harness appears to be OK, observe the "Idle Up Volume" display on the scan tool with ignition ON and engine OFF while moving connectors and wiring harness related to the switch. A change in the display will indicate the location of the fault.

DTC P1594

Schematic Reference: Engine Controls Schematics

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