heres the wiring diagram for the circuit.

HERE'S THE COMPLETE PIN POINT TEST FOR CODE P0155

H30 DTCS P0135, P0141 and P0155 AND P0161: HO2S HEATER CIRCUIT IS OPEN, SHORTED TO GROUND, SHORTED TO VPWR OR EXCESSIVE CURRENT DRAW

• • DTC P0135 = HO2S HTR-11
  • DTC P0141 = HO2S HTR-12
  • DTC P0155 = HO2S HTR-21
  • DTC P0161 = HO2S HTR-22
  • Shorts to VPWR in harness or HO2S.
  • Water in connectors.
  • Cut or pulled wires.
  • Disconnected wiring.
  • Open VPWR circuit.
  • Open GND circuit.
  • Low battery voltage.
  • Corrosion or poor mating terminals.
  • Damaged HO2S heater.
  • Damaged PCM.

Diagnostic Trouble Codes (DTCs) P0135 P0141, P0155 and P0161 indicate a short to ground, open, or short to VPWR in the HO2S heater circuit.

DTC/HO2S Reference List:

Possible causes:

Note: On some applications, a vehicle hoist is required to access the HO2S harness.

• Visually inspect the HO2S circuit for exposed wiring, contamination, corrosion and proper assembly.

Were any concerns found during the visual inspection?

H31 PERFORM KEY ON ENGINE OFF (KOEO) SELF-TEST

• Scan Tool connected.
• Key on.
• Run engine at 2000 rpm for 1 minute.
• Key off.
• Key on, engine off.
• Perform KOEO Self-Test.
• Key off.

H32 CHECK VPWR VOLTAGE TO H02S HARNESS CONNECTOR

Note: If DTCs P0135 and P0155 or P0141 and P0161 are displayed, both heater circuits will require testing. DTCs displayed separately are tested individually.

• Disconnect the appropriate HO2S(s).
• Key on, engine off.
• Measure voltage between VPWR circuit and SIG RTN circuit at the HO2S harness connector(s) (refer to schematic at the beginning of this Pinpoint Test).

Is the voltage greater than 10.5 volts?

H33 CHECK VPWR CIRCUIT FOR OPEN IN HARNESS

• Key off.
• Install breakout box. Leave PCM disconnected.
• Measure resistance of the VPWR circuit between PCM test pin 71 and VPWR circuit at the HO2S harness connector.

Is the resistance less than 4.0 ohms?

H34 CHECK HO2S HEATER RESISTANCE

• Measure the resistance of the HO2S heater (refer to schematic at the beginning of this Pinpoint Test).

Is the resistance between 3 and 30 ohms?

H35 CHECK HO2S CASE FOR SHORT TO VPWR AND HEATER GND

• Measure resistance between HO2S Heater GND at HO2S connector and the HO2S case.
• Measure resistance between the HO2S Heater GND and the SIG RTN Pin at the HO2S sensor.
• Measure the resistance between the HO2S VPWR at the HO2S connector and the HO2S case.

Is the resistance greater than 10,000 ohms?

H36 CHECK HO2S HEATER CIRCUIT FOR SHORT TO VPWR AND GND

• Disconnect Scan Tool from DLC.
• Breakout box installed, leave PCM disconnected.
• Refer to the HO2S Connector Pin Number Charts in the beginning of this section for Heater Ground Pin Numbers.
• Use the following list to measure the resistance between the appropriate test pins at the breakout box:
  • DTC P0135 = HO2S HTR-11 (HTR GND)
  • PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.
  • DTC P0141 = HO2S HTR-12 (HTR GND)
  • PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.
  • DTC P0155 = HO2S HTR-21 (HTR GND)
  • PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.
  • DTC P0161 = HO2S HTR-22 (HTR GND)
  • PCM Heater Ground Pin and PCM Test Pins 24, 103, 91 and 71.

Is the resistance greater than 10,000 ohms?

H37 CHECK HO2S HEATER GROUND FOR OPEN IN HARNESS

• Refer to the HO2S Connector Pin Number Charts in the beginning of this section for Heater Ground Pin Numbers.
• Use the following list to measure resistance between the appropriate PCM test pins at the breakout box and the HO2S HTR GND at the vehicle harness connector:
  • HO2S HTR-11=PCM Heater Ground Pin (HTR GND)
  • HO2S HTR-12=PCM Heater Ground Pin (HTR GND)
  • HO2S HTR-21=PCM Heater Ground Pin (HTR GND)
  • HO2S HTR-22=PCM Heater Ground Pin (HTR GND)

Is the resistance less than 4.0 ohms?

I hope this helps you out

mike