Test Ho2S - Heated Oxygen Sensor

Fig 1: HO2S Circuit & Connector Terminals ID

CIRCUIT PIN IDENTIFICATION

Circuit	Breakout Box Pin No.	PCM Pin	Wire Color
GND	46	3D	Black/Blue
Left HO2S	43	2D	Blue/White
Right HO2S	29	2C	Black/Yellow

NOTE: This test is intended to diagnose HO2S circuit only. On 2.5L, enter this test only when Code 15, 17, 23 or 24 is displayed during self-test procedures (KOEO or KOER). Code 15 or 17 indicates left HO2S malfunction. Code 23 or 24 indicates right HO2S malfunction. Code 15 or 23 indicates continuous output voltage of less than .55 volt (lean condition). Code 17 or 24 indicates HO2S feedback system does not change (rich condition) and may indicate condition other than HO2S circuit malfunction.

1) Check System Integrity Visually check wiring, connector and component for evidence of damage, shorting or looseness. If a fault is found, repair as necessary. If no fault is found, go to next step.

2) Check HO2S Sensor Output Voltage Turn ignition off and install breakout box. Connect PCM to breakout box. Warm engine to normal operating temperature. Measure voltage at HO2S test pin at breakout box. Compare voltage reading with HO2S VOLTAGE SPECIFICATIONS table below. If voltage readings are as specified, go to step 7). If readings are not as specified, proceed to the next step.

HO2S VOLTAGE SPECIFICATIONS

Condition	Voltage
Application	0.5-1.0
Deceleration	0-0.5
Idle (Cold)	0
Idle (Warm)	0-1.0
KOEO	0

3) Check HO2S Ground (2.5L) Turn ignition off. Disconnect HO2S sensor connector. Measure resistance ground and GND terminal at HO2S connector. If resistance is less than 5 ohms, go to step 5). If resistance is 5 ohms or more, repair sensor GND wire.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 3) to step 5). No test procedures have been omitted.

5) Check For Open HO2S Wire Ensure ignition is off and HO2S is disconnected. With breakout box installed and PCM disconnected, measure resistance between HO2S test pin at breakout box and HO2S terminal at HO2S connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in HO2S wire.

6) Check For Short In HO2S Wire Ensure ignition is off and HO2S is disconnected. With breakout box installed and PCM disconnected, measure resistance between ground and HO2S test pin at breakout box. If resistance is more than 10,000 ohms, replace HO2S. If resistance is 10,000 ohms or less, repair short to ground in HO2S wire.

7) Check HO2S Heater Resistance If voltage readings were okay in step 2), turn ignition off. Disconnect HO2S connector. With sensor at 68°F (20°C), measure resistance between terminals PWR and GND at HO2S. If resistance is about 6 ohms, go to next step. If resistance is not about 6 ohms, replace HO2S.

8) Check Power To HO2S Sensor Heater Turn ignition on. Measure voltage at PWR terminal at HO2S connector. If voltage is more than 10 volts, go to step 10). If voltage is 10 volts or less, go to TEST VPWR. If VPWR circuit is okay, repair VPWR wire to HO2S.

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 8) to step 10). No test procedures have been omitted.

10) Check HO2S Heater Ground If voltage was more than 10 volts in step 8), turn ignition off. With HO2S disconnected, measure resistance of HO2S heater GND wire between ground and HO2S connector. If resistance is less than 5 ohms, HO2S circuit is okay. If no other problem or code is found, replace PCM. If resistance is 5 ohms or more, repair sensor heater GND wire.