Oxygen Sensor Codes P0135,P0141,P0155

I have a 1996 Ford Bronco. I am getting the P0135, P0141 and P0151 Oxygen Sensor codes. I found it odd that all three would go bad at the same time, but a mechanic told me it was possible, so I replaced all three. The codes are back.

After reading some forums on the web as well as discussions here, it is suggested that it could be power to the Sensor heaters or even the PCM. I set the ignition switch to Run, disconnected one of the Sensors, and tested the (2) white wire connections with a test light. I have power at both white connectors. I have found the PCM and removed it to see if there was anything obvious and to maybe have it tested to see if it is good. Any suggestions on what else to try. Will a Ford dealer be able to test and re-program if needed? Any/all help is greatly appreciated.

Yes, the discussion on the 1998 Ford Taurus is nearly identical to your problem(s) with your 1996 Ford Bronco. Most of the wiring, and controls, and wiring diagram are nearly the same. The wiring diagram for your Bronco is here: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280180d52 Click on Fig. 24, and enlarge, download and print.

The DTCs P0135, P0141, P0155 are for the oxygen sensor heaters for each of the three oxygen sensors. There are two front, and one rear (downstream) oxygen sensor. On the wiring diagram, sensor 11 and 21 mean the front ones, and 12 means (bank 1) rear (2)sensor. ADDED: Your Bronco doesn’t show a code for the rear oxygen sensor heater. But, it does have a lean code (P0151).

The black/white wires don’t only ground the oxygen sensor heaters; they provide ground for all of the PCM. This is why you measure (ohms, or voltage drop) is made from one side (PCM pins 93, 94, 95) to the output (PCM pins 24, 38,51, 76, 77). If the PCM is in the Oxygen sensor heater-ON-mode, there won’t be any difference between the sides (across the PCM).

Download, and print, the discussion on Sordid Tale… If afterwards, you have further questions, come on back.

The wiring diagram wire colors to the oxygen sensors are for the wiring before the electrical connector to the oxygen sensors. The wires directly attached to the oxygen sensor are different colors on replaced oxygen sensors.

OMG! Not another one. This is incredible. If you follow the Sordid Tale… thread http://community.cartalk.com/posts/list/1326611.page you will understand why I say that.

Normally I would never say this without testing but since Hellokit and I have just been down this road I predict you are going to have to replace the PCM in order to fix this. You could check to see if you have voltage on pins 93,94,95,and 96 when you turn the key to RUN. If you do, the PCM is most likely bad. The PCM turns on the heaters by switching on a ground to those pins. Reprogramming the PCM isn’t going to fix this problem.

You have removed the PCM for examination. I doubt that you will see any physical defect; but, you can try.
Could someone check those particular circuits, of the oxygen sensor heater circuits, on a removed PCM (engine computer)? Someone capable, yes.

Ford says that the PCM power relay MUST be used when power is applied to the PCM. The PCM needs the resistance of the PCM power relay.

Power (12 volts), from the PCM power relay, would be applied to three oxygen sensor placed in series to each PCM pin 55, 71, 97. Even under test, the oxygen sensors get HOT! (600F degrees); so use caution. PCM pins 24, 25, 38, 51, 76, and 77 would be connected to the ground side.

During the first 10 seconds to 1 1/2 minuets, there will (should) be continuity between PCM power pins (93, 94, 95) and The PCM ground pins; and the oxygen sensor heaters heat get HOT, HOT, HOT!. After that 10 seconds to 1 1/2 minuets period, the path through the PCM is shut down, and the heaters stop heating.
Now, if I’m not confused, I’ve not been trying!

hellokit, cougar, thanks for all of your help. It is greatly appreciated. What I ended up doing was going to the local salvage yard, and found a Bronco that I could not determine what year it was (too many parts missing), however according to the build tag, it was a few months away from mine. I took out the computer and compared the tear tags, with the attached spread sheet I found online and it proved to be the same year. Mine was a Tin3, this one is a Tin1. I figured for the $25.00 cost of the PCM, it was worth a try. Since this truck is not a daily driver, I wanted to give it time for the codes to come back up. So far, (knock on wood), they have not come back on.

Unfortunately, on to the next vehicle with codes. My 17 year old son wrecked and totaled the only vehicle (1998 GMC Jimmy) I have that had no codes. The Bronco still has the ABS light on, but I understand I need a different scanner to diagnose that problem, but it will have to wait until I get the other (2) fixed. I will be starting new threads on those (1997 T-Bird and 2000 Maxima), and maybe you two will be able to offer assistance again. Thanks again.

I’m glad you have solved the problems with your 1996 Ford Bronco; but, I think you missed the point of our discussion, which was: “Troubleshoot a problem, rather than throw expensive parts at the symptoms”. Why? Though you may throw enough expensive parts at a problem for a cure, that is no guaranty of a fix; AND, you’ll be poorer for it.
Make a separate post for each vehicle you have a problem with, including the ABS (Anti-lock Brake System). There are a lot of able, knowledgeable, people who read these post who should be able to advise you.

You’re welcome for the help DDD. I think the Bronco will be good to go and you were wise to just try and swap out the ECU since the price was so low on the replacement unit and we had already worked on the other similair issue. The fella that has the similar problem as yours is still working on it and hasn’t been able to replace the ECU yet due to a mixup in the order for a replacement.

Sorry to hear about the damage to the GMC. We will be glad to help you out later on the other issues if you need it.

I have a 96 Ford Bronco 5.0L with the same problem, 135,141,155 fualt code i had replaced two of the O2 sensors last yr so when I got these code i replaced the third one hoping they would all go away but they didnt. I have a Few questions for you if you could help me. Where is the PCM I was read it was by the drivers side wheel well or by the emgency foot brake, Im assuming it has a 90pin conector on it. Is there a PCM relay that could be at fault and is your bronco still running with out any problems with the O2 sensor codes. I cant find the PCM on the autoparts sites is this part only availiable at the salvage yard. Thank you for your help