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DTC P0131: 1/1 O2 Sensor Shorted To Ground: Testing

CAUTION: To diagnose this DTC properly, manufacturer recommends allowing vehicle to sit overnight in order to have a totally cold engine. At time of testing, coolant temperature must be within 10 degrees of ambient air temperature or test results may not be accurate.
NOTE: 1/1 HO2S may also be referred to as an upstream oxygen sensor. On Federal models, 1/1 HO2S is located in exhaust downpipe in front of catalytic converter. On Calif. models, 4.0L 1/1 HO2S is located in front exhaust manifold. On 4.7L, 1/1 HO2S is located in left (driver's side) exhaust downpipe in front of catalytic converter.
  1. Turn ignition on. Using scan tool, read DTCs. If DTC SPECIFIC GOOD TRIP counter is displayed and displayed count is "0", go to next step. If DTC SPECIFIC GOOD TRIP counter is not displayed or displayed count is not "0", go to step  6 .
  2. Turn ignition on, with engine off. Using scan tool, read and record 1/1 HO2S signal voltage. Disconnect 1/1 HO2S connector and note voltage reading. If voltage changes from less than one volt to about 5 volts, replace 1/1 HO2S. If voltage does not change from less than one volt to about 5 volts, go to next step.
  3. Turn ignition off. Disconnect PCM connectors. PCM is located on firewall in right rear corner of engine compartment. Visually inspect connectors for corroded, damaged, pushed-out or miswired terminals. Repair connectors as necessary. If connectors are okay, measure resistance between Black/Light Blue wire and Light Green/Red wire at 1/1 HO2S connector. If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, Black/Light Blue wire is shorted to Light Green/Red wire. Repair wiring as necessary.
  4. Measure resistance between ground and Light Green/Red wire at 1/1 HO2S connector. If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short to ground in Light Green/Red wire between 1/1 HO2S and PCM.
  5. At this time, PCM is assumed to be defective. Replace PCM.
  6. Turn ignition off. Visually inspect related connectors and wiring harness for damage. Repair connectors and wiring harness as necessary. If connectors and wiring harness are okay, reconnect all connectors. Start engine. Wiggle 1/1 HO2S connector and wiring harness while monitoring scan tool display. If GOOD TRIP counter display count changes to "0", repair connector or wiring harness where wiggling caused display to change. If GOOD TRIP counter display count does not change to "0", no problem is indicated at this time. Check for any related technical service bulletins that may apply.
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