DTC P0130, P0131, P0132, P0133, P0136, P0135, P0136, P0137, P0138, P0140, P0141, P0150, P0151, P0152, P0153, P0156, P0157, P0158, P0160, P161, P1129, P1170, P1173: Ho2S Circuit Malfunction: Description

There are 4 Heated Oxygen Sensors (HO2S) located in the exhaust system. Front HO2S (bank 1, sensor 1) is located in front of the left side catalytic converter. Rear HO2S (bank 1, sensor 2) is located after the left side catalytic converter. Front HO2S (bank 2, sensor 1) is located in front of the right side catalytic converter. Rear HO2S (bank 2, sensor 2) is located after the right side catalytic converter. Rear HO2S measure oxygen content after catalytic converters to monitor operating efficiency of converters.

Each HO2S is electrically heated to ensure sensor achieves operating temperature as quickly as possible after start-up. ECM energizes HO2S heater using a Pulse Width Modulation (PWM) signal which starts low and increases within 30 seconds to desired heater temperature. Primary HO2S heaters are wired in parallel and secondary HO2S heaters are wired in parallel for synchronous ECM control of each heater pair.

HO2S operating temperature is approximately 662°F (350°C). To achieve and maintain this temperature there is a heating element incorporated in HO2S which is controlled by a PWM signal from the ECM. The HO2S heating elements are activated immediately after engine start or during low engine load conditions when exhaust gas temperature is insufficient to maintain the required HO2S operating temperature. If the heater fails, the ECM will not allow closed loop fueling to be implemented until the sensor has achieved the required operating temperature. This value equates to an HO2S output signal of 450-500 mV. A richer mixture will increase HO2S output voltage towards 1000 mV. A leaner mixture decreases HO2S output voltage towards 100 mV. From cold start, ECM runs an open loop fueling strategy. ECM keeps this strategy in place until the HO2S is at a normal operating temperature. At this point the ECM starts to receive HO2S information and it can then switch into closed loop fueling as part of its adaptive strategy. The maximum operating temperature of the HO2S tip is 1706°F (930°C), temperatures greater than this will damage the sensor.

In the event of a HO2S signal failure any of the following symptoms may be observed:

Default to open loop fueling on defective bank.
ECM will eventually default into open loop fueling.
High CO reading.
Excessive emissions.
Strong hydrogen sulfide smell like a strong smell of rotten eggs until the ECM defaults to open loop fueling.
MIL will be illuminated.

HO2S can fail in the following ways or supply incorrect signal:

HO2S sensor open circuit.
Short circuit to battery voltage.
Short circuit to ground.
Sensor disconnected.
Stoichiometric ratio outside the correct operating band.
HO2S contamination from leaded fuel or other source.
Air leak into the exhaust system.
Wiring harness damage.
Sensors installed incorrectly or cross wired.

NOTE: Front and rear HO2S sensors are not interchangeable even though they can be mounted in reversed positions. The harness connections are different: Orange in front and Gray in rear. Connector signal terminals are gold plated and heater supply terminals are tin plated. Interchanging terminals will cause contamination and adversely affect system performance.

If front HO2S wiring is crossed over (LH bank to RH bank), engine will run normally after initial start up, but performance will become progressively worse as sensors go towards maximum rich for one bank of cylinders and maximum lean for the other. If front HO2S wiring is switched left for right, vehicle will operate properly until sensors reach operating temperature. ECM will then cause one bank of cylinders to run very rich and the other bank to run very lean. This will cause engine to misfire, idle rough and emit black smoke, with possible catalytic converter damage.