Electrical Load Idle-Up Signal Diagnosis

Circuit Description

The powertrain control module (PCM) receives an electrical load idle-up signal when the rear defogger or the parking lamps are turned ON. The PCM increases the flow of air through the idle (bypass) air passage of the idle air control valve when receiving the electrical load idle-up signals. The additional air flowing through the idle air passage causes an increase in the idle speed. The idle speed is increased in order to accommodate the increased engine electrical loads.

Diagnostic Aids

The Electrical Load parameter on the scan tool can indicate if the PCM has received the rear defogger or parking lamps ON signal. The scan tool should indicate Yes when the rear defogger or parking lamps are turned ON and engine speed should increase slightly. Check for a malfunction in the IAC system or a short to ground in the Diagnostic Request circuit if the engine speed does not increase.

A malfunctioning rear defogger or parking lamp (taillight) circuit may cause erratic electrical load idle-up circuit performance. Check for a properly operating rear defogger or taillight system.

An intermittent malfunction may be caused by a fault in the electrical load idle-up signal electrical circuits. Inspect the wiring harness and components for any of the following conditions:

^ Backed out terminals.
^ Improper mating of terminals.
^ Broken electrical connector locks.
^ Improperly formed or damaged terminals.
^ Faulty terminal to wire connections.
^ Physical damage to the wiring harness.
^ A broken wire inside the insulation.
^ Corrosion of electrical connections, splices, or terminals.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

1. The OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step checks whether the PCM responds to the operation of the rear defogger. The IAC Duty Cycle percentage and the idle speed will increase when the rear defogger is turned ON if the idle-up system is OK.
3. This step checks whether the PCM responds to the operation of the taillights. The IAC Duty Cycle percentage and the idle speed will increase when the taillights are turned ON if the idle-up system is OK.
5. This step checks for an open or a short in the rear defogger switch circuit to the PCM. If the electrical circuit to the PCM is OK, repair the fault in the rear defogger circuit.
7. This step checks for an open or a short in the taillight switch circuit to the PCM. If the electrical circuit to the PCM is OK, repair the fault in the taillight circuit.
8. This step checks for a short to ground in the Diagnostic Request circuit A short to ground in the Diagnostic Request circuit can cause the PCM to ignore the rear defogger switch and the taillight switch inputs. A short in the Diagnostic Request circuit will cause the IAC duty cycle and the idle speed to remain fixed.