Mechanics

CHEVROLET S-10 HEATER PROBLEM

2003 Chevrolet S-10 • 70,000 miles

How to repair code po155
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December 27, 2012.




CIRCUIT DESCRIPTION
The heated oxygen sensor (HO2S) must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the powertrain control module (PCM). The PCM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The PCM determines the temperature by measuring the current flow through the heater. When the heater is in the ON state, the PCM will pulse the heater OFF for a duration of 50 ms, once per second. When the heater is in the OFF state, the PCM will pulse the heater ON for a duration of 50 ms, once per second. The PCM also monitors the current flow through the heater for diagnosis. This diagnostic will only run once per ignition cycle. If the PCM detects that the current is above or below a specified range, DTCs P0135, P0141, or P0155 sets.

CONDITIONS FOR RUNNING THE DTC

DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0442, P0446, P0452, P0453, P0455, P0496 are not set.
The ECT Sensor parameter is more than 50°C (122°F).
The Ignition 1 Signal parameter is between 10-18 volts.
The MAF Sensor parameter is between 3-40 g/s.
The Engine Speed parameter is between 500-3,000 RPM.
The Engine Run Time parameter is more than 120 seconds.

CONDITIONS FOR SETTING THE DTC

The PCM detects that the affected HO2S Heater current parameter is more than 2.5 amps or less than 0.25 amps.
The above condition is met for 10 seconds.

ACTION TAKEN WHEN THE DTC SETS

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

ASEMaster6371
Dec 27, 2012.


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