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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 39 (Engine Controls - Tests W/Codes - 5.2L CNG) >> Self-Diagnostic Tests >> Test TC-8A - O2S Stays At Center (DTC 21)

Test TC-8A - O2S Stays At Center (DTC 21)

WARNING: This page is about a different car, the 1995 Dodge Ram Wagon, 1995 Dodge Ram Van, 1995 Dodge Pickup, and 1995 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.
  1. Start engine. Apply parking brake. Allow engine to reach normal operating temperature. Using scan tool, set engine speed to 1500 RPM and read Oxygen Sensor (O2S) state. If O2S is locked at center, go to step 6). If O2S is not locked at center, observe scan tool display while wiggling O2S connector and wiring harness.
  2. If O2S at any time locked at center, repair defective wiring harness or O2S connector. Perform TEST VER-2.
    NOTE: An intermittent open O2S signal circuit (Black/Dark Green wire) will cause this condition.
  3. If O2S did not lock at center, condition required to set DTC is not present at this time. O2S STAYS AT CENTER DTC sets if O2S output voltage stays at .5 volt for 1.5 minutes with engine temperature more than 170°F and engine running for 2 minutes. Possible causes are open O2S signal circuit (Black/Dark Green wire) or failed sensor.
  4. Inspect all related wiring and connectors, and repair as necessary. Perform TEST VER-2. If wiring and connectors are okay, condition that initially set DTC has just been simulated. Perform following additional checks to assist in identifying a possible intermittent problem.
  5. Visually inspect related wiring harness connectors for broken, bent, pushed-out or corroded terminals. Visually inspect related wiring harnesses for chafed, pierced or broken wires. Check all related Tech Service Bulletins (TSBs) and perform corrective action as necessary. Test is complete. Perform TEST VER-2.
  6. Turn ignition off. Disconnect and inspect O2S connector. Repair as necessary. Using scan tool in ohmmeter mode, check resistance of O2S connector, sensor ground circuit (Black/Light Blue wire). If resistance is more than 5 ohms, repair open in Black/Light Blue wire. Perform TEST VER-2.
  7. If resistance is less than 5 ohms, connect a jumper wire between O2S connector, O2S signal circuit (Black/Dark Green wire) and positive battery post. Turn ignition on. Using scan tool in voltmeter mode, read O2S voltage. If voltage is more than one volt, replace O2S. Perform TEST VER-2. If voltage is less than one volt, turn ignition off.
  8. Disconnect and inspect Powertrain Control Module (PCM) connector for damaged, pushed-out or miswired terminals. Repair as necessary. Perform TEST VER-2.
  9. If connector is okay, disconnect jumper wire. Using an external ohmmeter, check resistance of O2S signal circuit (Black/Dark Green wire) between PCM connector terminal No. 41 and O2S connector. If resistance is more than 5 ohms, repair open in Black/Dark Green wire or Dark Green/White wire. Perform TEST VER-2. If resistance is less than 5 ohms, replace PCM. Perform TEST VER-2.
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