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For 1990-2009 cars only
Makes 🢒 Geo 🢒 1996 🢒 Metro 🢒 Engine 🢒 Engine Controls - 1.0L 🢒 Electrical/Accessory Load Idle-Up Signal Diagnosis

Schematic Reference: Engine Controls Schematics

Circuit Description

The powertrain control module (PCM) receives an electrical load idle-up signal from the diode module. The electrical load idle-up signal is present whenever one or more of the following systems is turned ON (operating):

    • Headlights
    • Rear Window Defogger
    • Heater Blower Motor

The idle speed control (ISC) motor increases the throttle valve opening in order to compensate for the additional electrical load.

Diagnostic Aids

A short to ground of the BRN/YEL wire may cause an open in the TAIL fuse.

Check for a faulty electrical connection to the PCM.

An intermittent malfunction may be caused by a fault in the electrical load idle-up circuit. 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 Powertrain 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.

  2. This step checks for the electrical load idle-up signal to the PCM.

    3.

  3. This step checks for each electrical input to the diode module.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: If the rear defogger, parking lamps or blower motor do not operate, diagnosis those components first.

  1. Install a scan tool.
  2. Start the engine.
  3. Run the engine until normal operating temperature is attained.
  4. Turn OFF all accessories.
  5. Monitor the electrical load parameter on the scan tool while turning the above electrical systems ON and OFF.

Does the scan tool indicate ON when the accessories are turn to ON and then OFF when the accessories are turn to OFF?

--

Electrical Load Idle-Up system is functioning normally

Go to Step 3

3

Did the engine speed increase with at least one of the accessories turned ON?

--

Go to Step 7

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the PCM electrical connectors.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Probe the electrical load idle-up signal circuit to ground (harness side) with a test lamp.
  5. Turn the Light Switch to Park or Head.

Did the test lamp illuminate?

--

Go to Step 5

Go to Step 6

5
  1. Check for faulty terminal connections at the PCM.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 10

Go to Step 9

6
  1. Check for an open in the electrical load Idle up signal circuit between the PCM and the diode module.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 10

Go to Step 8

7

Check the applicable system(s) that did not cause an increase in the engine speed.

    • Check the blower speed selector switch for a faulty connection or an open in the PNK/BLK wire to the diode module.
    • Check the light switch for a faulty connection or an open in the RED/YEL wire to the diode module.
    • Check the rear defogger switch for a faulty connection or an open in the RED/WHT wire to the diode module. Refer to Wiring Repairs in Wiring Systems.

Were any repairs necessary?

--

Go to Step 10

Go to Step 8

8

Replace the diode module. Refer to Diode Module Replacement .

Is the action complete?

--

Go to Step 10

--

9

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 10

--

10

Operate the vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

--

System OK

Go to Diagnostic Aids