Downstream Ho2S

DTC P1137, P1138 DETECTION CONDITION AND POSSIBLE CAUSES

DTC P1137, P1138	DOWNSTREAM HO2S
DETECTION CONDITION	The downstream HO2S is forced rich and lean by the PCM. The test fails if the PCM does not detect the output of the HO2S during KOER Self Test in a calibrated amount of time.
POSSIBLE CAUSE	Wiring concerns: Pinched, shorted, and corroded wiring and pins. Crossed sensor wires. Other concerns: Exhaust leaks. Contaminated or damaged sensor.

DTC P1137, P1138 INSPECTION

STEP	INSPECTION		ACTION
1	DTCS P1137 AND/OR P1138 INDICATE LACK OF HO2S SWITCHING Are any of the above possible causes present?	Yes	Repair as necessary. Go to step 9.
1		No	Go to step 2.
2	CHECK EXHAUST SYSTEM FOR LEAKS NOTE: Any exhaust leaks between the engine and the end of the catalyst can also cause DTCs P0136 and P0156. Key OFF. Place vehicle on hoist, transmission in PARK, emergency brake applied, raise vehicle. Inspect the following: Exhaust flanges for leaks. HO2S torque. Check for punctures and cracks in catalyst and pipes leading to them. Are there any exhaust leaks?	Yes	Replace or repair as required. Go to step 9.
2		No	Go to step 3.
3	CHECK HO2S HARNESS CIRCUIT FOR SHORT TO VPWR AND GROUND Disconnect NGS Tester from DLC. Disconnect PCM. Install Breakout Box. Leave PCM disconnected. Disconnect suspect HO2S. Measure resistance between HO2S signal circuit PCM test pin and SIG RTN circuit PCM test pin. Measure resistance between HO2S signal circuit PCM test pin and PWR GND circuit test pin. HO2S-12 = test pin 35 HO2S SIG RTN = test pin 91 PWR GND = test pins 24 and 103 Is the resistance greater than 10,000 ohms?	Yes	Go to step 4.
3		No	Repair short in harness. Go to step 9.
4	CHECK RESISTANCE OF HO2S AND HO2S GROUND CIRCUITS Measure resistance of HO2S signal circuit PCM test pin and the HO2S vehicle harness connector. Measure resistance of SIG RTN circuit between PCM test pin and HO2S SIG RTN vehicle harness connector. HO2S-12 SIG = test pin 35 HO2S SIG RTN = test pin 91 Is the resistance reading less than 5.0 ohms?	Yes	Go to step 5.
4		No	Repair open circuit. Go to step 9.
5	CHECK HO2S CIRCUIT VOLTAGE Connect PCM. Suspect HO2S connected to vehicle harness. NGS Tester connected. Key On Engine Off (KOEO). NOTE: Note: HO2S displayed as O2S on NGS Tester. Access the correct HO2S PID. Key OFF. Was the voltage greater than 1.5 volts?	Yes	Go to step 8.
5		No	Go to step 6.
6	CHECK RESISTANCE OF HO2S GROUND CIRCUIT IN THE PCM Connect PCM to Breakout Box. Vehicle harness disconnected from Breakout Box. Measure resistance between SIG RTN circuit PCM test pin 91 and PWR GND circuit PCM test pin 103. Is the resistance less than 5.0 ohms?	Yes	Remove Breakout Box. Reconnect PCM. Go to step 7.
6		No	Replace PCM. See POWERTRAIN CONTROL MODULE . Go to step 9.
7	APPLY 12 VOLTS TO SUSPECT HO2S CIRCUIT Suspect HO2S disconnected. Jumper VPWR to HO2S signal circuit at the HO2S harness connector. Key ON. Access HO2S PID and monitor. Is the PID value greater than 1.5 volts?	Yes	Replace HO2S. See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL & INSTALLATION article . Complete an HO2S Monitor Repair Verification Drive Cycle. See DRIVE CYCLES . Go to step 9.
7		No	Replace PCM. See POWERTRAIN CONTROL MODULE . Complete an HO2S Monitor Repair Verification Drive Cycle. See DRIVE CYCLES . Go to step 9.
8	CHECK FOR OVER VOLTAGE ON THE HO2S CIRCUIT IN THE PCM Key ON. HO2S disconnected. Measure voltage between SIG RTN circuit at the vehicle harness connector and battery negative post. Measure voltage of HO2S SIG circuit between HO2S vehicle harness connector and battery negative post. Are the voltage readings greater than 1.5 volts?	Yes	Replace PCM. See POWERTRAIN CONTROL MODULE . Go to step 9.
8		No	Replace HO2S. See HEATED OXYGEN SENSOR (HO2S) in REMOVAL, OVERHAUL & INSTALLATION article . Go to step 9.
9	Perform AFTER REPAIR PROCEDURE to ensure customer's concern has been resolved.