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For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2008 🢒 Isuzu MD F-Series 🢒 Body Systems 🢒 Lighting 🢒 Marker Lamps Inoperative

Marker Lamps Inoperative RPO RQ2, U86 or RQ3

Diagnostic Instructions
    • 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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

B+ -- Marker Lamp Relay

1

1

--

--

Marker Lamp Relay Control

1

1

2

--

Marker Lamp Control

1

1

2

--

Ground -- Marker Lamp Relay

--

1

--

--

B+ -- Marker Lamp Switch

1

1

--

--

Marker Lamp Switch LED Control

3

3

4

--

Ground -- Marker Lamp Switch LED

--

3

--

--

1. Marker lamps are inoperative

2. Marker lamps are always ON

3. Marker lamp switch LED indicator is inoperative

4. Marker lamp switch LED indicator is always ON

Circuit/System Description

Marker lamp relay coil is energized by B+ voltage when marker lamp switch is activated and switch contacts close to complete the circuit. Marker relay switch contacts close, providing B+ voltage to clearance and identification lamps, which in turn illuminate. Marker lamp switch LED illuminates when the switch is operated ON and is grounded at G400.

Reference Information

Schematic Reference

Exterior Lights Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. Headlamps ON, verify that the tail and marker lamps illuminate.
    2. ⇒If the tail or marker lamps do not illuminate, refer to Park, License, and/or Tail Lamps Malfunction .
  2. Ignition ON, command the marker lamps ON and OFF using the marker lamps switch. The marker lamps should turn ON and OFF when changing between the commanded states.
    3. ⇒If the marker lamps are always OFF or remain ON, refer to Marker Lamps Malfunction.
  3. Ignition ON, marker lamps ON, the marker lamp switch marker lamps ON indicator should illuminate.
    4. ⇒If the marker lamps ON indicator does not illuminate, refer to Marker Lamp Switch Indicator Malfunction.

Circuit/System Testing

Marker Lamps Malfunction

  1. Disconnect the harness connector at the marker lamp switch.
  2. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit terminal 1 and ground.
    3. ⇒If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the marker lamp switch and disconnect the MARKER LAMP Relay.
  4. Ignition OFF, test for less than 5.0 ohms between the relay coil ground circuit terminal and ground.
    5. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Verify that a test lamp illuminates between the relay B+ circuit terminal and ground.
    6. ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.
  6. Connect a test lamp between the marker lamp relay control circuit terminal and ground.
  7. Ignition ON, command the marker lamps ON and OFF using the marker lamps switch. The test lamp should turn ON and OFF when changing between the commanded states.
    8. ⇒If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, test or replace the marker lamp switch.
    ⇒If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the marker lamp switch.
  8. Connect a 10A fused jumper wire between the relay B+ circuit terminal and the relay switch output circuit terminal. The marker lamps should illuminate.
    9. ⇒If the marker lamps do not illuminate, test the output control circuit for an open/high resistance. If the circuit tests normal, test or replace the marker lamp relay.

Marker Lamp Switch Indicator Malfunction

  1. Ignition OFF, disconnect the harness connector at the marker lamp switch.
  2. Test for less than 5.0 ohms between the ground circuit terminal 4 and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Connect a test lamp between the control circuit terminal 3 and ground.
  4. Ignition ON, connect a 3A fused jumper wire between the ignition voltage circuit terminal 1 and the control circuit terminal 2. The test lamp should illuminate.
    5. ⇒If the test lamp does not illuminate, test the control circuit for an open/high resistance.
  5. If all circuits test normal, test or replace the marker lamp switch.

Component Testing
  1. Ignition OFF, disconnect the marker lamp relay.
  2. Test for 70-100 ohms between terminals 85 and 86.
    3. ⇒If the resistance is not within the specified range, replace the relay.
  3. Test for infinite resistance between the following terminals:
    4. • 30 and 85
    • 30 and 86
    • 30 and 87
    • 85 and 87
    ⇒If not the specified value, replace the relay.
  4. Test for less than 2.0 ohms between terminals 30 and 87A.
    5. ⇒If greater than the specified range, replace the relay.
  5. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2.0 ohms of resistance between terminals 30 and 87.
    6. ⇒If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Trailer Marker Lamp Switch Replacement
    •  Relay Replacement