2002 Maxima SE U1000 DTC error

[Gary_ket8r6f]

2002 Maxima SE, 110,000 miles.

I have a U1000 DTC code (usually followed by U1001, U1000) that I am struggling with.

I’ve located the ECM-F48, TCM-F51, F55 to M162, and the M15 to E81 SMJ connectors. I've cleaned them with electrical contact cleaner. I've cleaned and tightened the F39, F40, F41, and F42 ground connections to the engine.

While doing this I noticed that the F55 to M162 connector (below the radio area on driver’s side) had white tape around it. I also have some evidence, although it may be a coincidence that moving this connector around causes the U1000 error to go away for a while. After moving this connector I was able to drive 100 miles, and then sit for two days, then around 75 miles back (all with no errors) before getting the U1000 back. But this time with various O2 type errors. It was in this mode for a few a weeks where I can drive one or two small trips then I get U1000, U1001, and U1000 along with some combination of P0031, P0138, P152, P0158, P0132.

Currently I am getting U1000, U1001, U1000, and P132 pretty consistently.

I also notice that when I turn the ignition on, the AT light flashes 16 times and when I try to use cruise control the "Set" light flashes. At least once I notoiced that the crusie control worked when I had no check engine light errors, but I think I've seen the cruise set light flashing with no DTC errors.)

I assume I should ignore the AT light flashing, curise control Set light flashing, and all other DTC errors (ie P0031, P0138, P152, P0158, P0132) when acompanied with a U1000 error. Or can the P0132 error, for example, be a clue of as to why I have the U1000 error? I always have either no errors, or only U1000 errors, or U1000 and O2 type errors.

If the CAN communications (wiring and grounding) is solved, can I expect there to be no U1000 errors imeadiatly on my OBDII reader. For example, driving 175 miles with no errors then getting a U1000 along with an O2 error; Is it possible that the O2 error is real and the U1000 is from memory? (I'm assuming that if there is no DTC errors, then I get a U1000 code, that the CAN communication is bad. Period.)

I'm tempted to splice the two can wires at the ECM and TCM and jumpering them directly (from ECM to TCM) to bypass any possible intermittent connection in the factory harnesses. (I'm at wits end.) (Or alternately jumpering the CAN wires around the suspect F55 to M162 connector.)

Any advice would be appreciated.

I have an OINNOVA ODBII reader.

History: Last year I had a check engine light errors P0445 and P1448 and ended up paying $1000 to a local shop who replaced the cut valve, evap canister, gas cap, etc. It only stayed off a few months and now I have this new U1000 error. (I'm suspicious that they caused the U1000 in some way (loose wire or ground connection not tight? Possibly involving that white tape?)

[346ci]

U1000 and 1001 were usually caused by a poor ecm ground. If a Consult-II was used, the FF data would tell you this quick. Most don't have a Consult or acess to one though. If not, check the ECM grounds by removing their bolts/nuts and look at the mating surface to make sure they are making a good contact. The grounds are M14 and M78, both under the dash and get their ground though the cross brace. You could splice into the ECM's harness and "make" you own ground without having to check all that BS, just make sure it is a good ground. Maybe go to one of the front seat's track bolt.

The 02 sensor codes are common for your year/model. It would be best to have a Nissan dealer check those out. Most of the time the rear 02s need to be replaced and the ECM flashed for the updated parameters. They can check your current version also to see if a reprogram is even needed. Since yours is a '02, the middle 2 02 sensors should be the rears. You will see 4 02 sensor connectors in all. If you wanted to go cheap, you could replace the 02's and take it to a dealer for them to check your ECM's version. We only charged 1 hour of labor at the most to flash, usually only .5hr though. It's not hard or doens't take long if the Consult isn't tied up.

[Gary_ket8r6f]

Thanks 346ci,

I did not actually remove the ECM from its metal holder, but I tightened the four screws that secure the ECM into the holder (and they did seem loose.) I also removed, cleaned, and tightened the two screws that secure the ECM holder to the cross brace.

Once again the U1000 went away for two or three short trips then came back, this time with a new O2 error: U1000, U1001, U1000, P0171. A few days later P0171 was replaced with P0172.

Next step was to "make" my own ground to the passenger seat track bolt. With the battery disconnected and the ECM connector unplugged I measured the resistance from the six grounds I see listed for the EMC connector F48 (pins 48, 57, 78, 106, 107, 108.) All of them measured zero ohms except pin 78 which measured around .2 ohms. (The pin 78 ground signal travels through F68-M161, then M6-B3 before makings its way B13 ground. The other five grounds run directly to F41 or F42 which I have already cleaned and tightened.)
I ran two 12 AWG wires from an O ring terminal on the seat track bolt to the ECM area. I attached one of the grounds to the ECM holder bolt to the cross bar (with O terminal), and spliced the other ground wire in with the M78 ground wire (that was measuring .2 ohms to ground.)

I'm still getting U1000, U1001, U1000 (currently with no other error.)

I can also try removing the ECM completely and cleaning the surface between it and its metal holder (If I understand correctly "look at their mating surface.)

Would you suggest I splice and short together to the seat track all six ECM ground wires? (Or one from each set (ex: 48, 78, 106)?)

It seems like getting the thing on a Consult II is a good next step. Local shop has some kind of shop ODB II that has a key card for each kind of car. I assume that won’t help with my U1000.

[346ci]

I'm still getting U1000, U1001, U1000 (currently with no other error.)

I can also try removing the ECM completely and cleaning the surface between it and its metal holder (If I understand correctly "look at their mating surface.)

Would you suggest I splice and short together to the seat track all six ECM ground wires? (Or one from each set (ex: 48, 78, 106)?)

It seems like getting the thing on a Consult II is a good next step. Local shop has some kind of shop ODB II that has a key card for each kind of car. I assume that won’t help with my U1000.

You could try to connect all of them and then use a alligator clip to ground them to a well known ground. Just check that ground with a DVOM, go from the battery to that ground to check it. Sounds like you have them grounded good anyway. The next step I would take is to have it checked with a Consult. That scan tool the local shop has sounds like a Snap-On 2500 with the keys. That one might be ok if it can give the FF data for the U1000, U1001. You need to see what the freeze frame data is when those codes set.

When we worked on CAN codes, poor grounds and systems losing power seemed to be common. I used to drive the vehicles home with the Consult and read the live data, it could tell you when a system lost communication to another. Like the TCM lost comms with the PCM. You then played a wiring game to trace it or found a controller going out. CAN codes are tough without a Consult.

The ecm's surface to it's case should be fine. Not saying that is not the cause but I have never seen it.

I have repaired several of the O2 codes in those cars, never seen one have any relation to a U1000 or 1001.

[Gary_ket8r6f]

I left my car with Nissan, gave them a written histoy of my U1000 issue, and left them with the following written instructions:

1) Put the Consult II on and let me know what the FF data says about the U1000 error.
2) Let me know if the ECM needs a reflash.
3) Advise me of my options.

The bill was $99 for clearing the check engine light. Told me to drive it to see if it comes back.

I explained again that I am looking for the Consult II FF data. The guy at the counter talked to the tech again and returned with, "It will cost between $300 and $500 to just set up the Consult II. Then we will need to keep the car for one or two days." (They aren't willing to get me the Consult II information.)

To their credit they didn't charge me the $99.

Going to try more grounding, etc, then (assuming I still have the U1000) shop around for a local shop that is willing to accept my money in exchange for Consult II information. (I'm in the Waltham MA and Marlboro MA area.)

[Gary_ket8r6f]

I took the ECM out, roughed up the external surfaces with sand paper, opened it up, blew out the insides with canned air, ruughed up the ECM hoder where it mates. (I wasn't able to remove the holder. It was atached in the front middle in some way.)

I was starting to strip the four special ECM to holder screws and replaced them with little longer ones after verifying that the extra length did not appear to to do any internal damage.

Got it back together. Still runs Want to find some wire tapping connectors to tie the six grounds together as my final test before throwing in the towel

[346ci]

I explained again that I am looking for the Consult II FF data. The guy at the counter talked to the tech again and returned with, "It will cost between $300 and $500 to just set up the Consult II. Then we will need to keep the car for one or two days." (They aren't willing to get me the Consult II information.)

To their credit they didn't charge me the $99.

$300-$500 just to "set up" the consult II? What a bunch of F-tards. To read that code, it has already loaded all the data needed, including the FF data. All he had to do is hit print for the FF data, 2 seconds. Doesn't sound like they have any seasoned Nissan techs or any willing to help. I'd look for another shop....

[Gary_ket8r6f]

I'll call around for a local shop that can get me freeze frame data. In the mean time, more clues:

The only time the check engine light came on while I was driving, was U1000 + O2 codes.
Every time the check engine light came on with only U1000 (,U1001, U1000) was within 2 seconds of starting the car.
So the U1000 error only occurs at startup, or with an O2 error while driving.

I've also been cleaning O2 sensor connectors, plus added an injection cleaner to the gas tank, plus I've been doing a lot more highway driving and high rev driving, and I haven't seen any O2 errors in a while.

Now that I have the ECM clenaed up and bolted better, I'm only getting U1000 when starting the engine for the third (or more) trip.

This morning the engine light came on and my ODBII reported that all sensors (O2, evap, etc) were tested and good. But I had the U1000 error.
Unfortunatly (at least with my ODBII) clearing the U1000 casues the need to retest the sensors.

I may still try shorting the 6 ECM grounds to ground.
I may still try bypassing the two CAN wires between the ECM and TCM with direct wire.

[Gary_ket8r6f]

Since I am now only getting check engine light (U1000) while starting the car (and I have a sense that only when the car has been sitting awhile,) that the starting current from the battery "enables" the problem.

Weak battery?
Bad starter?
Again, some kind of poor grounding where, for example, more current = higher voltage at what is supposed to be ground? (ie ground at ECM or elsewhere looking like 0.2V instead of 0V?)

[Gary_ket8r6f]

Battery falls to 10.55 durring cranking No problem.

ECM ground pin # 78 rises to 0.005V with igition on or cranking.
ECM other ground pin (black with white) rises to .005 with ignition on, but 0.4V while cranking. Gotcha !!! I'm tying you down to the ground

[Gary_ket8r6f]

It turned out that ECM pin 78 (that was .2 ohms to ground) stays at 0.005V during engine cranking (good.)
The other five EMC ground pins (that measured 0 ohms to ground) were all jumping to 0.4V during cranking (sounds bad to me.)
(Since those five ground wires are supposed to go to F41 F42 on the top of the engine block, I wonder if the whole engine block is rising to 0.4V during cranking, meaning that the bad ground is between the battery and the block.)

I spliced into those five ground wires on the ECM cable and tied them to the seat slide bolt.

We shall see...

[Gary_ket8r6f]

346ci,

I did roughly 4 30 minute "trips" home from work with my new five wire grounding.
No U1000
No check engine light.
My ODBII says that all sensors are tested and okay.
I started the car up yet again, and same thing.

Looks promising. I'm going to walk out on a limb and add a Thumbs Up to both of us.
(We don't need no stinken Consult II , but it sure would have helped.)
(Were do I ship the case of beer? )

I'm going to get retested for my reject inspection in the morning (unless you think the ECM needs more time then 2 hours of driving to be ready (even thought my ODBII seems to say it is ready.)

Thanks man.
Gary

[346ci]

346ci,

I did roughly 4 30 minute "trips" home from work with my new five wire grounding.
No U1000
No check engine light.
My ODBII says that all sensors are tested and okay.
I started the car up yet again, and same thing.

Looks promising. I'm going to walk out on a limb and add a Thumbs Up to both of us.
(We don't need no stinken Consult II , but it sure would have helped.)
(Were do I ship the case of beer? )

I'm going to get retested for my reject inspection in the morning (unless you think the ECM needs more time then 2 hours of driving to be ready (even thought my ODBII seems to say it is ready.)

Thanks man.
Gary

Sounds good, congrats. A complete cool down, like sitting overnight, and a good 30 minute drive should do it.

[Gary_ket8r6f]

Starting the car this morning after sitting overnight, U1000 came back after maybe 3 to 4 seconds.
I assume this is because it takes more current to crank a cold engine and/or it takes longer to start the engine.

I had measurred the delta voltage between the batery negitive terminal and the engine block while cranking yesterday and it was .17V, almost half of the .4V I was seeing at the ECM. Going to look at the battery ground cable.

You mentioned sitting overnight and then a 30 minute trip before bringing it down for the retest. Is the sitting for many hours something that the ECM looks for (and required for passing inspection?) It certainly was a good check if my fix is robust.

I would like to bring the car in for a retest later this aftermoon without the "sitting overnight" unless you tell me it is best to wait for the morning.

[Gary_ket8r6f]

Just to close out this post:

I got my inspection sticker this morning by clearing the ECM, drove 10 min "trip 1", shut off engine, waited 10 sec, started engine (seems to not U1000 when engine is warm) drive an hour to inspection station, verify with my ODBII that system is ready, Passed inspection.

So I still have an issue with U1000 only when starting a cold engine. If I learn anything or have any more questions, I'll start a new post.

Thanks 346ci