Ford Mustang (1999-2004) Service Manual: Inspection and Verification

1. The interior lighting system is a generic electronic module (GEM) controlled system.

2. Verify the customer concern by operating the interior lighting system.

3. Visually inspect for the following obvious signs of mechanical and electrical damage.

Visual Inspection Chart

Mechanical Electrical
  • Switch(es)
  • CJB Fuses:
  • 7 (20A)
  • 32 (15A)
  • 39 (5A)
  • Wiring harness
  • Connections
  • Lamps
  • Circuitry

4. If the concern remains after the inspection, connect the scan tool to the data link connector (DLC) located beneath the instrument panel and select the vehicle to be tested from the scan tool menu. If the scan tool does not communicate with the vehicle:

  • check that the program card is correctly installed.
  • check the connections to the vehicle.
  • check the ignition switch position.

5. If the scan tool still does not communicate with the vehicle, refer to the scan tool manual.

6. Carry out the DATA LINK DIAGNOSTIC TEST. If the scan tool responds with:

  • CKT914, CKT915 or CKT70 = ALL ECUS NO RESP/NOT EQUIP, refer to Section .
  • NO RESP/NOT EQUIP for GEM, go to Pinpoint Test A.
  • SYSTEM PASSED, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and carry out self-test diagnostics for the GEM.

7. If the DTCs retrieved are related to the concern, go to GEM Diagnostic Trouble Code (DTC) Index to continue diagnostics.

8. If no DTCs related to the concern are retrieved, proceed to Symptom Chart to continue diagnostics.

GEM Diagnostic Trouble Code (DTC) Index

DTC Description Source
B1322 Driver Door Ajar Circuit Short to Ground GEM
B1330 Passenger Door Ajar Circuit Short to Ground GEM
B1334 Decklid Ajar Rear Door Circuit Short to Ground GEM
B1342 ECU Is Defective GEM
B1397 Power Door unlock Circuit Short to Battery GEM
B1405 Driver Power Window Down Circuit Short to Battery GEM
B1408 Driver Power Window Up Circuit Short to Battery GEM
B1410 Driver Power Window Motor Circuit Failure GEM
B1426 Lamp Safety Belt Circuit Short to Battery GEM
B1428 Lamp Safety Belt Circuit Failure GEM
B1431 Wiper Brake/Run Relay Circuit Failure GEM
B1432 Wiper Brake/Run Relay Circuit Short to Battery GEM
B1434 Wiper Hi/Low Speed Relay Coil Circuit Failure GEM
B1436 Wiper Hi/Low Speed Relay Coil Circuit Short to Battery GEM
B1438 Wiper Mode Select Switch Circuit Failure GEM
B1441 Wiper Mode Select Switch Circuit Short to Ground GEM
B1446 Wiper Park Sense Circuit Failure GEM
B1448 Wiper Park Sense Circuit Short to Battery GEM
B1450 Wiper Wash/Delay Switch Circuit Failure GEM
B1453 Wiper Wash/Delay Switch Circuit Short to Ground GEM
B1458 Wiper Washer Pump Motor Relay Circuit Failure GEM
B1460 Wiper Washer Pump Motor Relay Coil Circuit Short to Battery GEM
B1462 Safety Belt Switch Circuit Failure GEM
B1466 Wiper Hi/Low Speed Not Switching GEM
B1473 Wiper Low Speed Circuit Motor Failure GEM
B1476 Wiper High Speed Circuit Motor Failure GEM
B1551 Decklid Release Circuit Failure GEM
B1553 Decklid Release Circuit Short to Battery GEM
B1555 Ignition Run/Start Circuit Failure GEM
B1687 Lamp Dome Input Circuit Short to Battery GEM
B2486 LF Side Repeater Lamp Output Circuit Failure GEM
B2488 RF Side Repeater Lamp Output Circuit Failure GEM
C1189 Brake Fluid Level Sensor Input Short Circuit to Ground GEM
C1223 Lamp Brake Warning Output Circuit Failure GEM
C1225 Lamp Brake Warning Output Circuit Short to Battery GEM

Symptom Chart

Condition Possible Sources Action
  • No communication with the generic electronic module
  • CJB Fuse 39 (5A)
  • GEM.
  • Circuitry
  • GO to Pinpoint Test A .
  • The courtesy lamps are inoperative
  • CJB Fuse 7 (20A).
  • Door ajar switch (es).
  • Courtesy lamp assemblies.
  • Circuitry.
  • GEM.
  • Ignition Switch.
  • Headlamp Switch.
  • GO to Pinpoint Test B .
  • The demand lighting is inoperative
  • CJB Fuse 7 (20A).
  • Circuitry.
  • GEM.
  • Door ajar switch (es).
  • Demand lamp assemblies.
  • Ignition Switch.
  • Headlamp Switch.
  • GO to Pinpoint Test C .
  • The illuminated entry is inoperative when using the remote transmitter
  • Remote transmitter.
  • GEM
  • GO to Pinpoint Test D .
  • The battery saver does not deactivate after timeout
  • Circuitry.
  • GEM.
  • GO to Pinpoint Test E .
    Principles of Operation
    Battery Saver The battery saver feature provides automatic shut-off of power to demand and courtesy lamp circuitry. When the generic electronic module (GEM) detects the ignition switch circuits ...

    Pinpoint Tests
    CAUTION: Before removing and installing the GEM or its connectors, disconnect the battery. Failure to follow this caution will result in the GEM storing many erroneous DTCs and may result in the ...

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