Contour Enthusiasts Group Archives Forums General Troubleshooting CEL Code P0155 Question

My check engine light went on Yesterday. I went to Autozone and the code checked out to:

P0155 - 02 SENSOR CIRCUIT MALFUNCTION (BANK 2 SENSOR 1)

Is this one of those things that might be "a loose screw or wire" or is there more to it?

On a related note, I have noticed that if I let of the gas and the car idles down to below 2000 rpm, then the car accelerates in a herky jerky motion when I step back on the gas up to about 3000rpm. Is this normal or maybe even related to the above problem?

This fault is for the upstream O2 sensor in the front exhaust manifold. It could be a loose or intermitent connection, but it's very likely a dying sensor. This one is fairly easy to reach from the top. A new O2 sensor is like $60 at your local parts store and should come with the connector so all you have to do is unbolt the old one, screw in the new one, and swap plugs. You can remove this one with just a wrench, iirc.

The jerking could be a couple of things, but a clean fuel and air filter would be things to check along with the spark plugs.

Fuel filter is $10 and can be changed with just a scewdriver or 8mm nutdriver. (It under the car just in front of the PS rear wheel well)

Thanks. Would a recent exhaust replacement affect this at all?

The following is from the Ford Technical Service Publication (TSP):

P0135=Upstream Heated Oxygen Sensor Heater (HTR 11) circuit malfunction (Bank #1)
P0141=Downstream Heated Oxygen Sensor Heater (HTR 12) circuit malfunction (Bank #1)
P0155=Upstream Heated Oxygen Sensor Heater (HTR 21) circuit malfunction (Bank #2)
P0161=Downstream Heated Oxygen Sensor Heater (HTR 22) circuit malfunction (Bank #2)

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 B+ 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 PCM.

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

NOTE:
On some applications, a vehicle hoist may be required to access the HO2S harness.