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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Mazda B4000, 2003 Mazda B3000, and 2003 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed and KOEO or KOER DTC P0135, P0141 and P0155 were not present, fault may be intermittent. See INTERMITTENT  testing under SYSTEM TESTS. For other DTCs, go to next step.
  2. Visual Inspection -  Visually inspect suspect HO2S harness for exposed wiring, contamination and corrosion. If harness is okay, go to next step. If harness is not okay, repair as necessary. After repair, go to step  8 .
  3. Check For VPWR At Vehicle Harness Connector -  If DTCs P0135, P0155 or P0141 are displayed, both heater circuits will require testing. DTCs displayed separately are tested individually. Disconnect appropriate HO2S 4-pin harness connector. With KOEO, measure voltage between VPWR circuit (Light Blue/Orange wire) and SIG RTN circuit (Orange wire) at suspect HO2S 4-pin harness connector. See Fig 1 . If voltage reading is more than 10.5 volts, go to next step. If voltage reading is 10.5 volts or less, check No. 41 TRANSMISSION, EMISSIONS fuse (20-amp) located in engine compartment fuse/relay box. If fuse is okay, repair open circuit. After repair, go to step  8 . If fuse is not okay, replace fuse. After repair, go to step  8 .
    Fig 1: HO2S Harness Connector Circuit Identification
    G95E35968Courtesy of MAZDA MOTORS CORP.
  4. Check HO2S Heater Resistance -  Turn ignition off. Measure resistance of HO2S connector (component side) heater circuit (DTC P0135, Red/White wire), (DTC P0141, Red/Light Green wire) or (DTC P0155, Yellow/Light Blue wire). If resistance is 3-30 ohms, go to next step. If resistance is not 3-30 ohms, replace faulty HO2S. Go to step  8 .
  5. Check For Heater GND & VPWR Shorted To HO2S Case -  Measure resistance between HO2S heater GND circuit (component side) (DTC P0135, Red/White wire), (DTC P0141, White/Black wire) or (DTC P0155, Yellow/Light Blue wire) and HO2S case. Record reading. Measure resistance between HO2S heater GND circuit (DTC P0135, Red/White wire), (DTC P0141, White/Black wire) or (DTC P0155, Yellow/Light Blue wire) and SIG RTN circuit (Orange wire) at HO2S 4-pin connector (component side). Record reading. Measure resistance between HO2S VPWR circuit (Light Blue/Orange wire) and HO2S case. Record reading. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, replace faulty HO2S. After repair, go to step  8 .
  6. Check For Shorts To Other Grounds & VPWR In HO2S Heater Ground Harness Circuits -  Disconnect scan tool from DLC. Disconnect PCM 104-pin harness connector. Connect breakout box to PCM harness connector only. See Figure . For DTC P0135, measure resistance between breakout box terminal No. 93 and terminals No. 103, 91 and 71. For DTC P0141, measure resistance between breakout box terminal No. 95 and terminals No. 103, 91 and 71. For DTC P0155, measure resistance between breakout box terminal No. 94 and terminals No. 103, 91 and 71. For all DTCs, if resistance reading is more than 10,000 ohms, go to next step. If resistance reading is 10,000 ohms or less, repair short circuit. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  8 .
  7. Check For Open HO2S Heater Ground Harness Circuit -  For DTC P0135, measure resistance between breakout box terminal No. 93 and HO2S 4-pin harness connector (Red/White wire). For DTC P0141, measure resistance between breakout box terminal No. 95 and HO2S harness connector (White/Black wire). For DTC P0155, measure resistance between breakout box terminal No. 94 and HO2S harness connector (Yellow/Light Blue wire). See Fig 1 . For all DTCs, if resistance reading is 4 ohms or more, repair open (or excessive resistance) in HO2S heater circuit. After repair, go to next step. If resistance reading is less than 4 ohms, open, shorted or excessive resistance is present in HO2S heater circuit in PCM. Replace faulty PCM. After repair, go to next step.
  8. Verify Trouble Shooting Of DTCs Completed -  Make sure all electrical connectors are reconnected. Clear DTCs from PCM memory using scan tool. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If the same DTC is present, replace faulty PCM. After repair, repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no DTCs are present, test is complete.
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