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Pinpoint Test C: All Instrument Panel Illumination Does Not Dim

Refer to appropriate SYSTEM WIRING DIAGRAM article for Cluster and Panel Illumination schematic and connector information.

Normal Operation 

The smart junction box (SJB) monitors the input from the instrument panel dimmer switch by sending a voltage reference signal through circuit VLN18 (BU/WH) to the instrument panel dimmer switch. The return signal is sent through circuit CLN27 (WH/BN) back to the SJB. Based on the input from the instrument panel dimmer switch, the SJB sends a pulse-width modulated (PWM) voltage signal to the dimmable illumination sources. If the SJB detects a concern with the circuitry to the instrument panel dimmer switch, the SJB defaults the backlighting to a full intensity level.

The SJB also sends a message over the network to the audio control module (ACM), the rear entertainment module (RETM), the HVAC module - EATC, and the instrument cluster (IC) to indicate the backlighting intensity level. If the receiving module receives invalid backlighting data from the SJB for 5 seconds or less, the receiving module defaults the backlighting to the last setting.

If the receiving module does not receive the backlighting status message from the SJB or if the data received is deemed invalid for more than 5 seconds, the receiving module sets DTC U0140 in continuous memory (except the climate control module) and defaults the backlighting to full intensity.

This pinpoint test is intended to diagnose the following:

PINPOINT TEST C: ALL INSTRUMENT PANEL ILLUMINATION DOES NOT DIM 

CAUTION: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
NOTE: Calibrate the instrument panel dimmer switch by rotating the dimmer switch from the full dim position to the dome ON position before continuing diagnostics.
  1. C1 CHECK THE EXTERIOR LIGHTING OPERATION 
    • Place the headlamp switch in each of its positions while observing the exterior lamps.
    • Do the exterior lamps operate correctly? 
    1. YES  : Go to  C2.
    2. NO  : REFER to EXTERIOR LIGHTING article.
  2. C2 CHECK THE RECORDED RESULTS FROM BOTH CONTINUOUS AND ON-DEMAND SELF-TESTS 
    • Check for recorded DTCs from the continuous and on-demand self-tests.
    • Are any DTCs present? 
    1. YES  : If DTC B2212 is retrieved, go to  C4.

      For all other DTCs, REFER to MULTIFUNCTION ELECTRONIC MODULES article.

    2. NO  : Go to  C3.
  3. C3 CHECK THE INSTRUMENT PANEL DIMMER SWITCH INPUT 
    • Key in ON position.
    • Enter the following diagnostic mode on the diagnostic tool: SJB DataLogger
    • Monitor the SJB PID (DIM_SW_3) while rotating the instrument panel dimmer switch from the lowest setting to the highest setting.
    • Does the PID indicate the switch is operating correctly? 
    1. YES  : Go to  C9.
    2. NO  : INSTALL a new instrument panel dimmer switch. REFER to INSTRUMENT PANEL DIMMER SWITCH .
  4. C4 CHECK CIRCUIT CLN27 (WH/BN) FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: SJB C2280b
    • Disconnect: Instrument Panel Dimmer Switch C2298
    • Key in ON position.
      • Fig 1: Measuring Voltage Between Instrument Panel Dimmer Switch C2298-4, Circuit CLN27 (WH/BN) & Ground
      GF0032203Courtesy of FORD MOTOR CO.
    • Measure the voltage between the instrument panel dimmer switch C2298-4, circuit CLN27 (WH/BN), harness side and ground.
    • Is any voltage indicated? 
    1. YES  : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : Go to  C5.
  5. C5 CHECK CIRCUIT VLN18 (BU/WH) FOR A SHORT TO VOLTAGE 
      Fig 2: Measuring Voltage Between Instrument Panel Dimmer Switch C2298-6, Circuit VLN18 (BU/WH) & Ground
      GF0032204Courtesy of FORD MOTOR CO.
    • Measure the voltage between the instrument panel dimmer switch C2298-6, circuit VLN18 (BU/WH), harness side and ground.
    • Is any voltage indicated? 
    1. YES  : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
    2. NO  : Go to  C6.
  6. C6 CHECK CIRCUIT CLN27 (WH/BN) FOR AN OPEN OR A SHORT TO GROUND 
      Fig 3: Measuring Resistance Between Instrument Panel Dimmer Switch C2298-4, Circuit CLN27 (WH/BN) & SJB C2280B-33
      GF0032205Courtesy of FORD MOTOR CO.
    • Measure the resistance between the instrument panel dimmer switch C2298-4, circuit CLN27 (WH/BN), harness side and the SJB C2280b-33, circuit CLN27 (WH/BN), harness side; and between the instrument panel dimmer switch C2298-4, circuit CLN27 (WH/BN), harness side and ground.
    • Is the resistance less than 5 ohms between the instrument panel dimmer switch and the SJB, and greater than 10,000 ohms between the instrument panel dimmer switch and ground? 
    1. YES  : Go to  C7.
    2. NO  : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
  7. C7 CHECK CIRCUIT VLN18 (BU/WH) FOR AN OPEN OR A SHORT TO GROUND 
      Fig 4: Measuring Resistance Between Instrument Panel Dimmer Switch C2298-6, Circuit VLN18 (BU/WH) & SJB C2280B-34
      GF0032206Courtesy of FORD MOTOR CO.
    • Measure the resistance between the instrument panel dimmer switch C2298-6, circuit VLN18 (BU/WH), harness side and the SJB C2280b-34, circuit VLN18 (BU/WH), harness side; and between the instrument panel dimmer switch C2298-6, circuit VLN18 (BU/WH), harness side and ground.
    • Is the resistance less than 5 ohms between the instrument panel dimmer switch and the SJB, and greater than 10,000 ohms between the instrument panel dimmer switch and ground? 
    1. YES  : Go to  C8.
    2. NO  : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
  8. C8 CHECK THE INSTRUMENT PANEL DIMMER SWITCH 
    • Carry out the component test for the instrument panel dimmer switch. Refer to COMPONENT TESTING.
    • Is the instrument panel dimmer switch OK? 
    1. YES  : Go to  C9.
    2. NO  : INSTALL a new instrument panel dimmer switch. REFER to INSTRUMENT PANEL DIMMER SWITCH . TEST the system for normal operation.
  9. C9 CHECK FOR CORRECT SJB OPERATION 
    • Disconnect all the SJB connectors.
    • Check for:
      • corrosion
      • damaged pins
      • pushed-out pins
    • Connect all the SJB connectors and make sure they seat correctly.
    • Operate the system and verify the concern is still present.
    • Is the concern still present? 
    1. YES  : INSTALL a new SJB. REFER to MULTIFUNCTION ELECTRONIC MODULES article. TEST the system for normal operation.
    2. NO  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
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