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Home >> Dodge and Ram >> 2000 >> Ram Van B2500, Van Cargo Extended, 5.2 2 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Self-Diagnostics >> Diagnostic Tests >> DTC P0135: 1/1 O2 Sensor Heater Failure
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DTC P0135: 1/1 O2 Sensor Heater Failure

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION . For wiring diagram, see WIRING DIAGRAMS article.
NOTE: The 1/1 oxygen sensor may also be referred to as upstream oxygen sensor or primary oxygen sensor. 1/1 oxygen sensor heater is monitored when battery voltage is more than 9 volts, at a cold start, engine coolant temperature is less than 147°F (64°C), battery temperature is within 27 degrees of engine temperature and engine has been idling for at least 12 seconds. DTC may be stored in Powertrain Control Module (PCM) if 1/1 oxygen sensor voltage is more than 3 volts for 30-90 seconds. Possible causes are: defective 1/1 oxygen sensor or heater, defective Auto Shutdown (ASD) relay circuit, or defective connectors or wiring.
  1. Turn ignition on with engine off. Using scan tool, check for DTCs. If DTC SPECIFIC GOOD TRIP counter is displayed and equal to zero, go to next step. If DTC SPECIFIC GOOD TRIP counter is not displayed and equal to zero, go to step  5.
  2. Turn ignition off. Disconnect 1/1 oxygen sensor connector. The 1/1 oxygen sensor is located on exhaust pipe in front of catalytic converter. Turn ignition on with engine off. Using scan tool, actuate oxygen sensor heater test. Oxygen sensor heater test may also be referred to as O2 heater test. Using voltmeter, check voltage at terminal No. 1 (Dark Green wire on CNG models or Violet/Orange wire on gasoline models) on 1/1 oxygen sensor connector. If voltage is more than 11 volts, go to next step. If voltage is 11 volts or less, repair open on Dark Green wire (CNG models) or Violet/Orange wire (gasoline models) between 1/1 oxygen sensor and fuse No. 19/20 (10-amp for CNG models or 15-amp for gasoline models). Fuse No. 19/20 receives voltage from Auto Shutdown (ASD) relay. Fuse No. 19/20 and ASD relay are located in power distribution center at driver's side of engine compartment, near battery. Perform TEST VER-5 .
  3. Stop actuation of oxygen sensor heater test. Turn ignition off. Ensure 1/1 oxygen sensor connector is still disconnected. Using ohmmeter, check resistance between ground and terminal No. 2 (Black wire) on 1/1 oxygen sensor connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open on Black wire between 1/1 oxygen sensor and ground connection. Ground connection is located at firewall end of driver's side cylinder head. Perform TEST VER-5 .
  4. Using ohmmeter, check resistance of 1/1 oxygen sensor heater between terminals No. 1 and 2 on oxygen sensor side of 1/1 oxygen sensor connector. Terminals No. 1 and 2 are the 2 top terminals on the connector, closest to release latch on the connector. These terminals correspond with Dark Green wire (CNG models) or Violet/Orange wire (gasoline models) and Black wire on wiring harness side of 1/1 oxygen sensor connector. If resistance is 50 ohms or less, replace PCM. PCM is located on firewall, near brake booster. Perform TEST VER-5 . If resistance is more than 50 ohms, replace 1/1 oxygen sensor. Perform TEST VER-5 .
  5. Turn ignition off. Inspect wiring harness and connectors between 1/1 oxygen sensor and PCM. The 1/1 oxygen sensor is located on exhaust pipe in front of catalytic converter. PCM is located on firewall, near brake booster. Inspect 1/1 oxygen sensor connector and PCM connectors for corroded, pushed out, miswired or damaged terminals. Also, check for related Technical Service Bulletins (TSBs). If no problems and no related TSBs exist, test is complete. If any problems exist, repair wiring or connectors as necessary. Perform TEST VER-5 .
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