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Home >> Mazda >> 2001 >> MX-5 Miata Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Tests >> DTC P0140: Rear Ho2S Circuit, No Activity Detected >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

  1. Ensure FREEZE FRAME DATA has been recorded. Check for related service bulletins. Repair as necessary and go to next step.
  2. Turn ignition off and on. Using scan tool, check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If any other DTCs are present, go to appropriate test. If no other DTCs are present, go to next step.
  3. Check if DTC P0140 is present in FREEZE FRAME DATA. If DTC is present, go to next step. If DTC is not present, problem is intermittent. See TROUBLE SHOOTING - NO CODES article.
  4. Start and allow engine to warm to operating temperature. Using scan tool, access RHO2S PID data. Depress accelerator pedal to Wide Open Throttle (WOT) and release to race engine at 10 or more times. Scan tool should display RHO2S PID is more than .55 volt at least once during acceleration. If voltage is as specified, go to step  7. If voltage is not as specified, go to next step.
  5. Check rear HO2S installation. If no problem is found, go to next step. If problem is found, repair as necessary and go to step  9.
  6. Check for leaks in exhaust system upstream of rear HO2S. If problem is found, repair as necessary and go to step  9. If no leaks are present, check for open or short to ground on Red wire between PCM connector terminal No. 4AA and rear HO2S connector terminal "A". See Figure and Figure . Repair as necessary. If Red wire is okay, replace rear HO2S and go to step  9.
  7. Check cooling system for combustion gases. If no problem is found, go to next step. If combustion gases are found in cooling system, repair leak and go to step  9.
  8. Check engine compression. Engine compression should be a minimum of 146 psi (10.22 kg/cm2 ) at 300 RPM with a maximum variation of 28 psi (2 kg/cm2 ). If compression is as specified, go to next step. If compression is not as specified, repair as necessary and go to next step. If no problem is found, go to next step.
  9. Reconnect all connectors. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Start engine and allow it to reach normal operating temperature. Ensure engine coolant temperature is more than 176°F (80°C). Increase and hold idle speed at more than 1500 RPM for more than 54.2 seconds. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC P0140 is present, replace PCM and go to next step. On vehicles equipped with immobilizer system, reprogram ignition key identification numbers. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. If DTC P0140 is not present, go to next step.
  10. Cycle ignition from off to on. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to appropriate test.
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