The car was cold during these tests. I positioned the multimeter probes on the pcm and car-body ground, then I had my significant other insert the key and turn the car on (engine off). The meter would go wild for a split second and then drop to a steady 11.7v… I had her leave the car on for about 10 seconds per test.
I don’t know about the last question. I’ll look into it.
I want to clarify how the car acts once the battery has been disconnected. For all I remember, it has always done this.
During the first couple drives, the rpms will suddenly drop 2 or 3k and then surge back up to what they were. This will happen at highway speeds, even with cruise control on and no hills; and will occur in a period of about a second and a half.
The PCM or transmission controller may be going through some sort of relearning process after the battery is reconnected and the engine is running.
That rpm drop is a pretty severe re-learning step; but, there are other priorities. The battery voltage of 11.7 volts was low, maybe too low, for the oxygen sensor voltage drop test. You need to do it again, engine off. It can be done with the engine running if it’s done within 120 seconds of engine-on. Reference page 20 of this: http://www.motorcraftservice.com/vdirs/diagnostics/pdf/obdsm986.pdf
If the oxygen sensor heaters don’t work, you’ll need one of these: http://www.partsamerica.com/ProductList.aspx?PartType=248&PTSet=A
[ I don’t like those wide red bands on either side of the page. UGH! ]
Thanks for the great Ford reference material Hellokit. After reading about the DTC codes for P0135 and P0155 I still am unsure when the PCM actually turns on the heaters but if you go by the exhaust temps it looks like it may be after the engine has been running for a little while. The inferred exhaust temp minimum is 250 degrees.
If I was checking this out I would use one of the rear heaters as a reference since it is working ok. I would place the voltmeter leads across pin 95 or 96 and ground, start the engine and then time it to see when the voltage on the meter goes low (heater turns on). You will then have a reliable reference to a known good working circuit. As I keep saying though, I still think all this is going to come down to replacing the PCM.
Oxygen sensor heaters
The oxygen sensor heaters are turned ON the moment (or, within 5 seconds) that the engine is started. They heat for 2 minuets, and are then turned OFF. [Two minuets on this 1996-1999 era of Fords.]
The test data doesn’t indicate to us if the engine must be just started, or if it may be off, for the PCM to turn the heaters on. Mr. mfaerber did the test, as I/we requested, with the engine OFF. His test meter, set on volts, showed a momentary flutter, not (the hoped for) drop. The flutter may be meaning ful.
The rear oxygen sensor heaters (PCM pins 95, 96), which haven't set heater malfunction codes, should have shown a voltage drop [i]if[/i] the test method of key ON, engine OFF is valid. This is why we need the oxygen sensor heater voltage drop test done on a COOL engine, with the key just now turned to START, and the engine just now started, and the readings taken within [b]2[/b] minuets.I totally understand what you say there Hellokit. Would you point out to me where you saw the info about the heaters being turned on immediately? I didn’t see it and am curious as to where or how it is shown. After going over the info it looked to me that there may be a delay in the turn on time until the exhaust heats the sensors up to a minimum temperature of 250 degrees. It also looked to me that the ‘ON’ time duration is only for 2 minutes and the ‘MONITORING’ duration is for <5 seconds of that 2 minute period.
You are confusing the heater element of the oxygen sensor with the sensing element of the oxygen sensor. The heating element must heat the sensing element to over 250F degrees before the sensing element can begin sending its air/fuel ratio voltage to the PCM. When the sensing element begins sending the A/F information to the PCM, the PCM can begin controlling fuel, spark, additional air (iac), and so on ACTIVELY, not, from “best guesses”.
I’ve not shown all of the dozen, or so, information sources I’ve been to. So, I can’t always pinpoint a particular one.
There are oxygen sensors patented (in production?) that, using an incorporated heater, heat the oxygen sensor in 10 seconds! This gets undesired emissions under control much quicker, which helps us breathe greener.
Unfortunately, it is STILL raining here… I’m sure I’ll be able to do the test tomorrow though.
I’ve been hesitant to ask, but what is the worst case scenario for me? Is it a bad PCM, or something worse within the engine?
If the oxygen sensor heaters are setting DTCs, and it’s the PCM’s fault, to satisfy the Emissions Test requirement, you’ll have to replace the PCM.
Inside your PCM (engine computer) are switches for the oxygen sensors (one for each). Switches, in general, can have movable contact points, or, be electronic switches and have NO contacts. I don’t know which type are in your PCM.
If there are movable contacts for the oxygen sensor heaters, and they are burned, they could be sanded with very fine grit sand paper, and made to work.
If the switches are electronic, an electronic specialist may be able to do something.
Have the heater codes come back? I think it takes two “drive cycles” since last reset, for the DTCs (if present) to set.
All of the codes DID come back on, after about 10 miles of driving. I think I read somewhere that it only takes 5 miles for the O2 sensors to throw a code if something is wrong…
I promise I tried like hell to do the PCM tests with the engine on this morning, but poking little needles into little holes + torrential rain = FAIL… Would 4 hours of the engine being off (i.e. late tonight) be enough time for the engine to cool off for this test? I don’t think so…
And yes, the new site design sucks. Bad call to shrink the width of these forums.
I realize that my location can be up to 25,000 miles different from someone else’s; so that, whether weather is different, or whether weather is similar is dependent on whether one is near or far. (It’s clear, here).
So as not to confuse me, what are “all the DTCs that came back on”?
If the DTCs for the rear oxygen sensor heaters DID NOT come on, remember that for the test. If the test, later, is valid, the results of the rear heaters should be different from the front heaters.
The exhaust, and oxygen sensors, will be cool enough for testing if you can lay your hand on the exhaust and you don’t hear that SIZZLING sound (followed by words like, “Oh, heck! Ouchie!”)
[ I would love to be able to ask the PCM, “Why aren’t you turning the front oxygen sensor heaters ON?”]
Well the cat has been sitting here reading the posts again and thinking things over. At this point Matthew I think you would be ahead of the game if you ordered the proper PCM using the link that Hellokit very conveniently and thoughtfully provided. I think you will save yourself any time in further testing or possible frustration. The way I see it is replacing the PCM has a 98% percent chance of eliminating the heater problems. There may be something else causing this trouble but I sure don’t know what it is, if there is something else. I am confident all the connections for the circuit are ok.
To help verify the PCM is bad I can think of one other thing that we could try doing if you want to do that and it would be pretty easy to do. One trick I like to use sometimes when testing circuits, especially when they are duplicate circuits, is to check the resistance between the suspected trouble leads and ground, along with the power supply lead sometimes. This testing method has helped me pin down trouble at times. Using your ohmmeter set it to a fairly high resistance scale then test the PCM while it is disconnected from the vehicle wiring. Place the meter common lead on a PCM ground pin and then take readings of all four of the pins for the heaters and compare them to each other. You may also want to place the meter in the diode testing mode and check the pins that way in case there is a diode junction in the circuit. Look for a significant difference in readings between the pins for the front and rear heaters. If they are different this to me would say you have verified the trouble being inside the PCM.
Another poster, JAD2007, was having a similar problem with ignition coil switches ( called “drivers”) in his PCM. Mr. Cougar suggested the same type check he posed to you. Unfortunately, JAD2007 didn’t post if he performed the checks, or what the results were. He changed the PCM. Here’s the link to that post: http://community.cartalk.com/posts/list/21/1207214.page
I pulled the PCM wires out this morning before I hooked up the scan tool… Before I did that the light DID come back on. However, the last time I used the scan tool was BEFORE the light came on and it grabbed 2 PENDING codes: P0135 and P0155, both are O2 heater codes and there is no mention of lean or rich.
OK, I think I did a good job, but I can’t guarantee these results (I was rushed) and if they look funky to you, I’ll do them again. I only have 2 good “backprobes”, so I only tested two pins at a time and in between pairs I had the car turned off. So for each 2 pins I tested, the car engine was on for only about a minute. Now, that DOES mean that it took more than two minutes to accomplish this sequence: engine on -> read pins 93, 95 -> engine off -> pull pins out, stick them in 94,96 -> engine on -> read pins 94, 96. But the engine was never on for a whole two minutes at a time. So I hope these results count:
PIN:
93 = 170mv and gradually, steadily dropped
94 = 200mv and gradually, steadily dropped
95 = 14v, quickly dropped to 200mv and gradually, steadily dropped from there
96 = 50mv and gradually, steadily dropped
Note that for all of these backprobe tests, once I stick the backprobe in, I stick another pin in the corresponding hole of the PCM wiring harness and check the ohms with my multimeter to make sure that the first backprobe is making a good connection.
(I double checked what I just typed)
You did well Matthew. I assume you had the meter common probe tied to ground since you saw 14 volts for a brief time at least. From your readings we now have a ‘bit of a sticky wicket’ as our friends from across the pond would say. The low voltages on all the pins means all the heaters are now working, at least when you did the testing. I can only suggest try driving the car and see if the heater codes now go away.
SORRY TO SAY BUT YOU ARE BETTER OFF TAKING TO DEALER FOR CHECK ENGINE LIGHT,
TSB MAY APPLY, PLUS THE TECH AT DEALER GOT THE EXPERIENCE WITH YOUR VEHICLE,
PLUS THE DELAER GUARRANTEES WORK,
There was low voltage (low mV) on pins 93, 94, 95, 96 when the engine was turned ON; but, what about before then? Was there 12 plus volts on the pins when the ignition was turned to ON, with the engine off?
You didn’t report if there was.
Here is a very informative U.S. Patent for: “a diagnostic tool for sensing oxygen sensor heater operation”, by Delphi Technologies …a big supplier of the electronics in Fords: http://www.patentstorm.us/patents/7278414/description.html It’s in, mostly, standard English. You’ll have to register (easy and free) to see it all.