My service soon light came on and the code reads p0135 and p0155 o2 sensors. Heater circuit. I have replaced all four on both sides. Still the light comes on within two or three restarts.

What can I do from here? I checked wiring and seems to be fine.
The Snap On code reader showed both sensors near engine exhust manifold not working.

Could it be the PCM?

 

Capt Caper,

Here is what the Ford manual says about the DTC PO135. Thanks to SSCULLY.

P0135 - HO2S Sensor Circuit Malfunction (HO2S-11)
Description
During testing the HO2S Heaters are checked for opens /shorts and excessive current draw. The test fails when current draw exceeds a calibrated limit and /or an open or short is detected.

Possible Causes
-Short to VPWR in harness or HO2S.
-Water in harness connector.
-Open VPWR circuit
-Open GND circuit.
-Low battery voltage.
-Corrosion or poor mating terminals and wiring
-Damaged HO2S heater.
-Damaged PCM.

Diagnostic Aides
-wiring.
-Damaged HO2S heater.
-Damaged PCM.

The same would apply to your Bank 2 Sensor 1 PO155 code. Check those connecters for moisture/corrosion. Recheck the wires along their entire length for compromised insulation.

Good Luck,

Bill

 

Yes, it could be.

However, it is far more likely that there is a simple open circuit, short circuit, or other wiring fault that is causing the simultaneous error codes.

Consult the PCED on the service CD for your particular year and engine. It has a step-by-step procedure for troubleshooting the fault.

As you did not identify your vehicle by year and engine, it is not possible to give more exact information.

Steve

 

Steve

Sorry I thought my sig was posted. It is a 99 F150 4.6 W engine.

Were can I get a service CD?

I checked the connections again and wiring back to where it splits from the larger harness and I didn't see anything unusuall not to say I missed something.

After resetting the light it will come on at the 3rd restart. Seem's after resetting it and starting I can drive for quite a while and no light,but after shutting down and restarting for a 3rd. time it'll come back on.

Is there a way to check the PCM for this problem? I saw posted somewhere part of a PCM can go bad.

Capt.

 

You can buy copies of service CDs from ebay for under $10-15 for bootlegs.

I have sigs turned off since I don't feel like expending bandwidth downloadng pics of everybodies' trucks. Not that they aren't nice trucks, I just don't care to see them. Didn't even think of that

It takes the third consecutive drive cycle fors the computer to set the MIL. If you were to scan for pending codes after the first or second drive cycle, you would see the code as pending but the MIL would be off. Third time is the charm.

Get the schematic from the EVTM and the procedure from the PCED and see if the circuit is getting power and if the PCM is properly driving the low side of the heater circuit. Do this before assuming that you have a PCM fault as each heater has its own current sink. Since it's more likely that a common power source has failed than two separate sink circuits, focus on the power supply.

Steve

 

Thanks to all

I'll try these suggestions. My has the truck so I won't get to it for a while.

Capt.