P0155

CIRCUIT DESCRIPTION
The VCM supplies a voltage of approximately 0.45 volt (45 mV) between the HO2S High and the HO2S Low circuit.

If this voltage is measured using a 10 megohm digital voltmeter, the voltage may read as low as 0.32 volt. The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1.0 volt (1000 mV) if the exhaust is rich to as low as 0.10 volt (10 mV) if the exhaust is lean. When HO2S temperature is below 360°C (600°F), the sensor will not produce any voltage. The sensor will behave like an open circuit. This will result in an Open Loop operation.

The HO2S heater provides for a faster sensor warm-up which allows the sensor to become active in a shorter period of time and remain active during a long extended idle. The DTC P0155 determines if the HO2S heater is functioning properly by monitoring the amount of time necessary for the HO2S to become active after start-up. This DTCs is a type B DTC.

CONDITIONS FOR SETTING THE DTC
The following conditions will set the DTC:

1. The System Voltage is greater than 9 volts but less than 17 volts.
2. The MAF is less than 27 grams per second.
3. The Engine Coolant Temperature (ECT) is less than 32°C (90°F).
4. The Intake Air Temperature (IAT) is less than 32°C (90°F).
5. The difference between the ECT sensor and the IAT sensor is no more than 5°C (41°F).
6. The time for the HO2S (Bank 2, Sensor 1) in order to obtain ±150 mV from 450 mV is too great.

ACTION TAKEN WHEN THE DTC SETS
With a current DTC set, the VCM turns on the Malfunction Indicator Lamp (MIL) after 2 consecutive test failures.

CONDITIONS FOR CLEARING THE MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

DIAGNOSTIC AIDS
Check for the following conditions:

^ A poor connection
^ A damaged harness: Inspect harness connectors for the following situations:

1. Backed out terminals.
2. Improper mating.
3. Broken locks.
4. Improperly formed or damaged terminals.
5. Poor terminal to wire connection.
6. Damaged harness.

Never solder the HO2S wires. For proper wire and connector repair, refer to Wiring Repairs.

TEST DESCRIPTION
The numbers below refer to the step numbers in the diagnostic table.

2. This step determines if the DTC P0155 is the result of a hard failure or an intermittent condition. With the ignition ON and the engine off, the HO2S (Bank 2, Sensor 1) voltage displayed on the scan tool should gradually change to 0.150 volt, indicating that the heater is working properly. The HO2S voltage can rise as high as 975 mV before it toggles back down. The main thing to look for is a change.
3. Probing terminal D of the HO2S (Bank 2, Sensor 1) connector verifies if voltage is available to the HO2S (Bank 2, Sensor 1) heater.
4. If voltage is available at the connector, then it becomes a good voltage source to check for a ground at terminal C.
5. This step determines if voltage is not available at the HO2S (Bank 2, Sensor 1) due to an open fuse or open ignition feed circuit. If the fuse is open, determine if it was due to a short in the ignition feed circuit before replacing the fuse.