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Ok I just bought a bosch O2 sensor to replace the one I though had gone bad. I still get the same DTC even after replacement. Code says bank 2 sensor one cicuit fault. I have run both KOEO and KOER self tests and got DTC's P1000 in the KOEO and P1000 + P1705 in the KOER. I can't get any real reference to the P1705 since the service cd lists this code for manual transmissions in the contour/tracer. Is the sensor b4 the cat considered upstream or downstream? I assumed upstream since the sensor is b4 the cat, but if it is downstream the I bought the wrong sensor. I have checked all the wires I can see for cuts/shorts and found none. So this is eaither a PCM fault or Sensor fault. Anyong got any ideas?
Wes
 

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You did Erase the Codes, Correct? And yes, Upstream is the Fronts.
 

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Wes, you mention code P0155 (HO2S Sensor Circuit Malfunction - HO2S-21) in the thread sub-title and then you talk about a P1705 code in your post, which is not an O2-related code. P1705 = Transmission Range Sensor Out of Self-Test Range.

If it's P1705, try erasing the code and then see if it comes back. If it does, then you should think about a new TR Sensor.

If its P0155, then you are looking at the "Bank 2, Upstream" 02 Sensor which means its located somewhere on the cylinder bank exhaust that is closest to the front of the car, before the CAT.

You might want to save this link for future reference: Motorcraft DTC Search
 

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

DTC P0135 = HO2S HTR-11
DTC P0141 = HO2S HTR-12
DTC P0155 = HO2S HTR-21
DTC P0161 = HO2S HTR-22
Possible causes:

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.
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?
Yes
REPAIR any concerns found in the visual inspection. COMPLETE PCM Reset to clear DTCs. RESTORE vehicle. RERUN Quick Test .

No
GO to H31 .

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.
Are DTCs P0135, P0141, P0155 or P0161 present?
Yes
GO to H32 .

No
No DTCs present. Fault may be intermittent. GO to Pinpoint Test Step Z1 with the following data: HO2S PIDs and a list of Possible causes.

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?
Yes
GO to H34 .

No
GO to H33 .

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?
Yes
GO to H34 .

No
CHECK fuse in circuit. If fuse is OK, REPAIR open circuit. RESTORE vehicle. RERUN Quick Test .

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?
Yes
GO to H35 .

No
REPLACE HO2S. RESTORE vehicle. RERUN Quick Test .

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?
Yes
GO to H36 .

No
REPLACE HO2S. RESTORE vehicle. RERUN Quick Test .

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?
Yes
GO to H37 .

No
REPAIR shorted circuit. RESTORE vehicle. RERUN Quick Test .

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?
Yes
Open or shorted or excessive resistance in the heater circuit in the PCM. REPLACE PCM. RESTORE vehicle. RERUN Quick Test .

No
REPAIR open or excessive resistance in the heater circuit in harness. RESTORE vehicle RERUN Quick Test .
 
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