Majik

Okay Guys... I have searched my butt off and learned quite a bit about the dreaded P1688 code... But I have reached a point that I could use some opinions... So... Here is the situation:

About 5 months ago, I had a P1688 (The initial circuit check failure of MOP) code come up. I replaced it with a used one from Pineapple Racing, and the problem was gone... Up until about a week ago when once again, my car went into limp mode with the P1688 code. So I parked her, pulled the battery bay, and sprayed the crap out of the connectors (as well as pulled the PCM cap and checked all the connections). Let her sit a day, then re-connected everything, reset NVRAM, and fired her up... No CEL... Drove the crap out the car, with numerous shutdowns and startups (waiting about 10 minutes between start ups to emulate a fuel up). NO CEL.. I was able to do this for a few days, and then today it hit me again... Now, this time around, I drove her a bit, parked her, then uploaded a new map to the ECU. It was immediately after flashing an updated map (from Mazdamaniac) on my COBB AP that I got the CEL again!

From here, I debated the map being the culprit, so I un-married my COBB, and fired it up with stock ECU setting... NO CEL... So then I re-installed the Mazdamaniac map... NO CEL.. Drove her, turned it off, fired it up, NO CEL...

And now im here.... Clearly this isn't over.... So I am basically test driving the car over the next week to see if it comes back.... Which im sure it will...

What im looking for here is advice on my next attack? In other words, next time it pops up, should I attempt adjusting the sensor? Would an initial circuit test failure be related to that?? Should I order a new wire harness?? Or just get a whole new pump?? At this point, Ill be saving up for a new pump, so any advice in the meantime would be awesome!

Thanks.

NOTE: Im suspicious that this could be heat related?? Is it possible for the OMP to overheat?? Then work after its cooled a bit?

dannobre

iTrader: (3)

Where do you live?

Often the position switch doesn't throw a code...so it might be the actual pump that isn't right. Make sure that your connections are good...check the pins and connectors

Worst problems to troubleshoot are intermittent electrical issues

TeamRX8

iTrader: (25)

What do you have to lose by just adjusting the sensor switch and seeing what happens?

dannobre

iTrader: (3)

As long as it isn't creating a double fault....much harder to figure out ;-)

Harlan

iTrader: (3)

I'd place money on a bad connection in the harness.


The OMP switch is more than just a make or break switch, it has variable resistance to a point and then has a break over to high resistance. Someday when I'm bored I'll scope the output, but until then I can tell you this much: It tells the ecu some sort of OMP position.

Because of this it can fall out of tolerance just like the steering position sensor if the connectors get corroded. So, since you've already cleaned connectors (and replaced the pump) the next step is to split out the connector and solider the crimped connections. I just had to do this with my power steering connectors and it has fixed both PS and tracon. The OMP may be more susceptible to puddles because of it's low location.



Adjusting the sensor probably won't help. The OMP can either make it through the full range of the sensor or it can't, and if the sensor hasn't been moved since the factory I don't recommend moving it now because you could end up adding another problem as dannobre mentioned.

dannobre

iTrader: (3)

With the CEL...I would suspect the connector to the pump itself first...before the switch

I've never had a CEL with the position switch problem...usually just results in a limp mode problem

Majik

Im in Portland, OR.. And the problem first appeared on the hottest day we have had this year.. It hit 100 degrees F. The first time it popped the code I had shut her off for a fuel up after about a 45 minute city trip... And when it came back after the cleaning attempt a few days later, it was about 90 out, and the car had been drivin for about 30 minutes before I shut it off, then fired it up with the code...

Ill have to check those connectors again and see if I can spot something..

Majik

Im going to continue to tinker with the wiring for now and avoid the sensor adjustment for now... Does anyone know the part number for a replacement harness??

I should also note the pump I replaced was USED, so I suppose it could be going out as well (and I just lost a dice roll on a used part)..

dannobre

iTrader: (3)

The harness is part of the engine harness...so you would either have to repair it or buy a new or used one....they are pricey....so you might want to fix it if it is the issue ;-)

it is possibly the pump...you might want to try and get another one if the wiring isn't the issue

Harlan

iTrader: (3)

Ok, I tried pulling apart the plug on a spare harness and either I just don't have the touch today or the PS connectors are just easier. I can only imagine trying to do it while under the car.

Another option although not the best is to solider the harness directly to the omp position sensor. It's only connected by the two outside wires and polarity doesn't matter. You could even temporarily connect it with some test leads and see if that's your problem.

I'm still not convinced it's the pump, it's just a motor and a position sensor. Not a whole lot to fail, and doubtful it could have an intermittent failure. A mechanical failure would stop it permanently.

Oh and the connectors can look fine (even internally) and still be the problem. When I took apart my PS connectors everything looked shiny no obvious corrosion. But after soldiering them the problems went away, so there was some sort of problem there.

Majik

Im leaning this way as well! Thanks for the input! Im cranking out overtime all week and driving my truck for now, but I did get her out for a few 30 minute drives with no limp mode or cel so far.. Obviously it didn't just fix itself when I reflashed the ECU, so, this weekend I will be taking her over to my pops place (who happens to be an electrician) and Im gonna have him run the shop manual's recommended tests on the electrical stuff.. Then just for security, we are gonna pull the plug and solder the connections like you recommended...

Let me ask you tho... Should I do BOTH plugs? or just the sensor plug? You seem to be leaning towards that sensor plug as my possible culprit..

And a side note... When I DO get this solved.. I will be sure to post the good news and culprit for future seekers!

Harlan

iTrader: (3)

Both plugs wouldn't hurt, but if it's going to be the sensor plug that's the problem.

Majik

Just a quick update... I took her out for a nice cruise tonight after work.. It was around 75 degrees out, and she drove like a champ the whole 20 minute cruise until I got back to the garage and shut her down, then restarted her to see if it would throw the code... It did.

It seems to ONLY throw a code AFTER things heat up and are good and hot...

Anyways, still planning to solder the plug on Saturday, as well as inspect the ECU for damage as a precaution... I would REALLY like to avoid shelling out the $$ on a new MOP if I can...

Harlan

iTrader: (3)

Yeah my DSC/TC problem would only happen when it was started while hot. I don't know why the hot vs cold is a problem, but the car self checks several systems when it is initially started, the OMP being one of them. Your ECU is fine, just fix the plug and you should never see the code again.

Majik

Ok, plug has been pulled and soldered... It was a bitch, but I got it! Im currently taking a break from my test drives now.. Im 4 in with no cel so far... Im keeping my fingers crossed because it looked pretty clean when I pulled those wires... We will see!

I also tested the pump for resistance while I was in there and both connections yielded acceptable OHMS resistance according to the service manual specs.

I did however come across an interesting thing during this.. My negative battery cable could use a new terminal Im thinking... No matter how tight I get it, there is a small amount of play if I give it some ooomph to test its tightness.. The positive terminal is nice and snug tho.. But... Would a slightly (ever so slightly) loose negative connection cause a p1688??? Ill be replacing the terminals regardless, but just something that arose...

Majik

Meh... She threw up the p1688 and went into limp mode after the 8 or 9th restart... Replaced the battery terminals with no luck... Looks like Im still chasing the gremlin... I found a used pump from a guy who is parting out his car due to compression loss... It's cheap enough that Im gonna attempt swapping the MOP on my next step... Not sure how Im gonna deal with the wiring harness if thats it... I was peeking at it today, and that thing wraps all over stuff! Doesn't look like it would be easy to swap out..

Harlan

iTrader: (3)

PM me. I've got a spare OMP plug if you want to put it back, also have a spare OMP sitting around. At this point it might be grounds... I really hate electrical gremlins on this car.

Majik

To any following this.. I recently went to adjust the pump sensor, and discovered the screws were pretty loose... Not sure if that would cause anything, so I also pulled the pump out, and manually rewound it... Cleaned her up a bit, re-installed everything, and am now test driving her once again... Not gonna hold my breath.. If the cel returns, I will tweak the sensor a couple more times, then im throwing in the towel and ordering a new pump. Ill post any changes as usual.

I made a couple trips with her and started her up 4 times so far.. So its definitely too early to tell.. I did noticed with I pulled the motor that the stepping gear was not fully at the set screw.. Not sure if that would have been causing anything, but I reset it regardless..

Majik

Oh.. And inside the pump.. I discovered some white goop that didn't quite look like it belonged, I cant imagine grease being needed in this particular spot... Here's a pic... The pic is prior to cleaning so its pretty nasty lookin.. Sorry about pic quality... Phone shot