98 GT DTC P0135 - S1B1 heater

Start first by checking the fuses. Next check the connectors/wiring to the O2 sensors. The DTC is thrown because the PCM does not detect the O2 heaters are working.

Are you sure the correct O2 sensors were used for the application? There are similar O2 sensors with different wattage heaters. Using an incorrect O2 sensor could confuse the PCM.

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P0135 - HO2S Sensor Circuit Malfunction (HO2S-11)

• 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.

I am using a new pair of these:

NAPA AUTO PARTS

The heater is on the O2 sensor right? All it needs is power provided by the harness?

That sensor was damaged when I replaced it. Looked like when the motor mount failed, it crushed that O2. So I have them swapped out. No issues.

Keep in mind, I do have DPEF Error as well. Would that have any bearing on the DTC?

So you don't think it's possible that the wires were pulled and damaged?

Are there any other DTC's? Did you check the fuses?

Note some of the other "causes" listed. For example, "Open VPWR circuit.". This could be from a damaged wiring harness. The "Open GND circuit." could result from a pulled wiring harness as well.

Yes the heaters are in the O2 sensors.

Do you have an ODB2 scanner? If so, monitor the O2 sensor values. Do they change or remain in a very small value? Compare bank 1 to bank 2. Are the values close or really far apart?

If the heaters are working on the other (3) O2 sensors, then it's unlikely to be a blown fuse.

For detailed trouble shooting, look at diagram 024-007. Verify there is +12 volts with the key on the RED wire.

The other tests are more complicated. Basically ringing out the lines back to the PCM.

wmburns said:

So you don't think it's possible that the wires were pulled and damaged?

Are there any other DTC's? Did you check the fuses?

Note some of the other "causes" listed. For example, "Open VPWR circuit.". This could be from a damaged wiring harness. The "Open GND circuit." could result from a pulled wiring harness as well.

Yes the heaters are in the O2 sensors.

Do you have an ODB2 scanner? If so, monitor the O2 sensor values. Do they change or remain in a very small value? Compare bank 1 to bank 2. Are the values close or really far apart?

If the heaters are working on the other (3) O2 sensors, then it's unlikely to be a blown fuse.

For detailed trouble shooting, look at diagram 024-007. Verify there is +12 volts with the key on the RED wire.

The other tests are more complicated. Basically ringing out the lines back to the PCM.

Click to expand...

It's possible that the wiring harness did get pulled or smashed, but not very likely. The wires go a different direction from the area where the engine tweaked its way too. I will have to get back under the car and try to follow the wire back to it's splice point, but past that, itll require a ton of shelling and checking the wires.

You are correct, the other 3 work fine and don't complain of anything.

The only other DTC is the P1401, which is the DPFE Feedback High. Which..since this guy seemed to use some of the sensors from the P71 and some from the original engine it was on, I am betting he has the DPFE form the P71 and not the original mustang, causing the DTC.....

I had just wondered if that if DPFE codes might cause a heater code, tho doubtful.

I will also run a continuity test on the O2 sensor for the heater wires to see if it comes back resistance or OL. I guess it is possible that the heater circuit could have been bad right out of the gate, but again, doubtful.

From what I was reading, the white wires on the O2 sensor are the heater circuits. One of those wires with the key on would provide 12 volts, correct?

Look here....

NGK Spark Plugs USA

4 Wire Sensor states;

Black - signal
Gray - ground
White (x2) Heater

So which heater wire is gonna be the incoming power and the other the ground?! Sheesh...I would assume one would have 12 volts on it, and the other would not.......ideas?

I do have an OBDII scanner, its a Craftsmen and does NOT show PID's from sensors....I did buy a Bama tuner...dunno if it will show me the info or not.

Regarding the voltage question, most sensors in today's cars are "ground" start devices. This means that the circuit is controlled by completing the ground. This has a number of advantages and considerations.

The sensor is not turned on/off by the application of power. There is power available at a powered sensor when ever the key is on. That's why the 1st test is to CONFIRM power at the sensor.

As to how to tell WHICH wire does what, this is were the wiring diagrams are helpful. For the 1998 Mustang look at diagram 024-007. The wiring harness colors and connector pin numbers are shown. Note the +12 VPWR is present at the RED wire for all (4) O2 sensors.

With a ground start circuit it's possible to "test" the circuit by measuring/sensing at the open voltage on the return wire. The PCM is able to perform a basic circuit test all of the time. So when a DTC states "circuit malfunction" this basically means the PCM is not seeing a valid return "sense" open circuit voltage.

Soooooooooo. If the sensor itself is good, the connector is good, and the wiring harness is good, then the PCM must be bad.

Personally I would never replace a PCM until all other possibilities have been ruled out.

wmburns said:

Regarding the voltage question, most sensors in today's cars are "ground" start devices. This means that the circuit is controlled by completing the ground. This has a number of advantages and considerations.

The sensor is not turned on/off by the application of power. There is power available at a powered sensor when ever the key is on. That's why the 1st test is to CONFIRM power at the sensor.

As to how to tell WHICH wire does what, this is were the wiring diagrams are helpful. For the 1998 Mustang look at diagram 024-007. The wiring harness colors and connector pin numbers are shown. Note the +12 VPWR is present at the RED wire for all (4) O2 sensors.

With a ground start circuit it's possible to "test" the circuit by measuring/sensing at the open voltage on the return wire. The PCM is able to perform a basic circuit test all of the time. So when a DTC states "circuit malfunction" this basically means the PCM is not seeing a valid return "sense" open circuit voltage.

Soooooooooo. If the sensor itself is good, the connector is good, and the wiring harness is good, then the PCM must be bad.

Personally I would never replace a PCM until all other possibilities have been ruled out.

Click to expand...

You are super helpful as always.

So...I would assume the sensor may be bad, and I will try and rule it out. I will also test the 12+ on the red wire BUT, if the circuit wasn't being provided any power, you would get a DTC based on no sensor OR one of the lean/rich codes correct?

My whole idea on testing the heater circuits, or trying to figure it out, is locating a possible break in the wire. So, if I put a VM in the middle of the heater wires while the ignition is on, it should tell me if there is a complete circuit, or does the heater only come on when the car is running. But that also leads to the PCM not seeing the o2 sensor periode. Kinda a crappy situation.

There has to be a better way to test it.

The PCM knows the difference between certain failure levels. For example, the PCM will not call out rich/lean codes when the basic sensor tests fail. So once the circuit malfunction DTC is set, no further O2 tests are run as they would be invalid.

You method of testing will not work or give you the results that you think.

The most reliable first test is the one that you have been given. CONFIRM there is +12 volts present on the Red wire. This is a simple test done with a VOM on the red wire to a known good ground with the key on.

The next test should be to monitor the O2 sensor values with an ODB2 scanner (not a code reader). Why? In this case, we don't know if the heater is where the fault is. The fault could be in the O2 signal return lines.

Unless you like chasing wild geese, the best way to test this is by "ringing out" each of the wires back to the PCM on a "dead" circuit. This means REMOVING the PCM and using an Ohm meter to confirm a good circuit. If doing these tests, also check for a ground fault.

Trouble shooting wiring harness faults can be some of the hardest trouble shooting there is. Why? Because they are rare and each fault is different. This is why you shouldn't cut any corners on the visual inspection. A fair number of wiring faults can be located via a visual inspection.

Sounds pretty hardcore to shell all wires and follow them back to the PCM.

Could be a 5+ hour job with alot of potential for creating more problems.

If the heater circuit is failed in the o2, it would be an easy fix.

hrmf. this irks me greatly. So where do the endpoints run too? Cant i check cont back to that point?

The force is weak on this one. :laughlitt

You didn't honestly think anyone was suggesting that you "shell" all the wires back did you? No. The suggestion is to perform a visual inspection on the OUTSIDE of the wiring harness. Any external force that can damage the wires inside is also likely to leave evidence on the outside.

I guess that you don't understand how to "ring" out a wiring harness should it come to that. This is where the wiring diagrams pay BIG dividends. The wiring diagrams contain the connector and PIN#'s for all wires. Sooooooooo

Disconnect the negative battery terminal and remove the main PCM connector in the right hand fender well. Use the wiring diagrams to locate the wires PCM pin#. This will give two end points of the same wire. Now use the Volt-Ohm Meter (VOM) and a long piece of wire to make a resistance measurement. The Ohms should be low.

Now measure from the open wire to ground. This reading should be high. If not, this indicates a ground fault.

Yes removing the PCM is a PIA. But it's much easier than "shelling" a complete wiring harness on the car.

But all kidding aside, in previous posts you stated that you are positive that the connector is fine. No water damage. The sensor itself is good. Well if this were my car, the FIRST place I would look would be the O2 body harness connector. Especially when you stated there was wiring damage from broken motor mounts.

wmburns.....I swear you are awesome with this stuff. Sorry that I am a moron in some places. I'm still fairly new and get intimidated real quick when looking at those diagrams.

So, I live in Wyoming...its a desert climate. The chance of getting water in there is pretty slim, unless its coming from the engine.

Tho, I cleared the codes the other day, and I haven't seen the same error come up. Then again, I have been clearing codes every day for the P1401 (DPFE), so I need to tackle that first.

Thanks for explaining what you mean by ringing out the harness. I was expecting to do that but a guy I work with was telling me I was crazy to do so.

I found a few diagrams that are SUPER helpful for this.

https://sphotos-a.xx.fbcdn.net/hphotos-ash3/544726_10151229761567500_523983978_n.jpg

So I would assume the numbers in the PCM area are the pins.

So I wonder, when you look at the PCM, is it marked where the pins start? Is it right to left, top to bottom, or bottom to top, or left to right bottom to top, if you get what I am saying.

Again, I really appreciate your help. I am an idiot sometimes.

DPFE is fixed...time to drive it until something trips. I will keep you posted wmburns. Thanks again.

For the 1998 model year, diagram 024-007 is the O2 sensors. The diagram lists all of the connectors the wire passes through. The numbers in the the PCM block are the PCM pin numbers.

The PCM connector is C294. On the Ford wiring diagrams, push the "connector" button. Select with a "check mark" connector C294 for the 4.6 2v. This will bring a DIAGRAM of the connector face with the pins numbers displayed. No guessing about which way the pins are numbered.

Below the diagram will be the pin numbers, wire color, and circuit function. The 2nd page of the diagram is hard to find but it's under cell 150-068 and 150-069.

See, your the man. I would have had to hunt for that **** forever. Now I know exactly where I am going too find this.

I appreciate this dude. I really do.

I drove it for a while tonight, after replacing the DPFE, everything is gravy. Tho I wanna take it off and redo it with a longer hose......I kinda had to strech this one as the stock DPFE is positioned different.

Ugh, popped up again tonight. Weird this is it happened after driving it a while. So I wonder what happend to cause it. Cleared the code and awaiting the CEL again.

your o2 heaters will come on with key in on position,,

when its cooled off,,turn key on dont start it..crawl under and feel o2,,it should start getting hot...

when having 1 code,,you can swap o2 side to side..if code follows o2 its a bad o2..

code stays the same its other than o2..

when working with o2 codes it can take awhile for them reappear.

if you run engine at 2000rpms for 2 mins code should spit again without driving it..

sometimes the tool used to get codes can be wrong as in not giving codes when check engine light is lit,,,

also on the connector for o2 on main harness..all the pins are straight and even..and clean,,no black spots or discoloring