2003 Mazda B4000 Base, AutomaticFACTORY OEM SERVICE PROCEDURE

Malfunction Indicator Lamp

  1. Check For A No Start Condition -  If MIL is always on, go to next step. If MIL is not always on, go to step  3 .
  2. MIL Always On: Check MIL Circuit For Short To Ground -  If key on, KOEO or Continuous Memory DTCs are set, repair those DTCs before proceeding. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . Turn ignition off. Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance between breakout box terminal No. 2 (MIL circuit) and terminals 51 or 103 (PWR GND circuit). If resistance reading is less than 5 ohms, repair short circuit in Pink/Light Green wire between PCM 104-pin harness connector terminal No. 2 and instrument cluster 12-pin harness connector terminal No. 9. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. Rerun QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If resistance reading is 5 ohms or more, replace faulty PCM. Rerun QUICK TEST  under SELF-DIAGNOSTIC SYSTEM.
  3. MIL Never On -  With KOEO, measure voltage from negative battery terminal to ground side of instrument panel fuse panel No. 11 fuse (7.5-amp). Turn ignition off. If voltage reading is more than 10.5 volts, go to step  5 . If voltage reading is 10.5 volts or less, go to next step.
  4. Check For B+ At Fuse -  With KOEO, measure voltage between negative battery terminal to B+ side of fuse. Turn ignition off. If voltage reading was more than 10.5 volts, replace faulty fuse. Verify repair by turning ignition switch to ON position. If voltage reading is 10.5 volts or less, measure voltage from negative battery post to B+ side of instrument panel fuse panel No. 11 fuse (7.5-amp). Repair open B+ circuit. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS.
  5. Check For Voltage On MIL B+ Circuit -  Disconnect instrument cluster 12-pin harness connector. See Fig 1 . With KOEO, measure voltage between instrument cluster 12-pin harness connector terminal No. 9 (Pink/Light Green wire) and negative battery terminal. Turn ignition off. If voltage reading is more than 10.5 volts, go to next step. If voltage reading is 10.5 volts or less, repair open circuit in Pink/Light Green wire between instrument cluster 12-pin harness connector terminal No. 9 and PCM 104-pin harness connector terminal No. 2 through in-line connectors No. 124 and 135. Verify repair by turning ignition on.
    Fig 1: Identifying Instrument Cluster 12-Pin Harness Connector Terminals
    G00193649Courtesy of MAZDA MOTORS CORP.
  6. Check MIL Circuit Resistance -  Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector and PCM. See Figure . Measure resistance between breakout box terminal No. 2 (MIL circuit) and instrument cluster 12-pin connector terminal No. 9 (Pink/Light Green wire). If resistance reading is less than 5 ohms, go to next step. Verify repair by turning ignition on. If resistance reading is 5 ohms or more, repair open circuit in Pink/Light Green wire between 12-pin harness connector terminal No. 9 and PCM 104-pin harness connector terminal No. 2 through in-line connectors No. 124 and 135. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. Verify repair by turning ignition on.
  7. Check MIL Control Circuit -  Connect instrument cluster 12-pin harness connector. Turn ignition on. Connect a fused jumper wire (10-amp) between breakout box terminals No. 2 and 24. Observe MIL. If MIL does not illuminate, go to next step. If MIL illuminates, go to step  1 and repeat procedure. Something may have been missed during diagnosis.
  8. Check Pink/Light Green Wire For Open -  Turn ignition off. Disconnect instrument cluster 12-pin harness connector. Using a DVOM, measure resistance between breakout box terminal No. 2 (Pink/Light Green wire) and instrument cluster 12-pin harness connector terminal No. 9 (Pink/Light Green wire). See Fig 1 . If resistance reading is less than 5 ohms, replace faulty instrument cluster printer circuit. Verify system operation. If resistance reading is 5 ohms or more, repair open circuit in Pink/Light Green wire through in-line connectors No. 124 and 135. Verify system operation.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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