Working on an 04 6spd with 41k miles.. Dealing with a P1688 code thats causing the ecu to put the car into limp mode. I inspected the connectors for the oil metering pump and they were secure with no corrosion on the pins. I replaced the oil metering pump with a known good one that I had on the shelfand replaced the rubber gasket and crush washers. Engine started and ran great and code instantly came back and was in limp mode within 10 seconds. Engine ran for about 15 minutes at idle and I backed the car out of the garage and it was no longer in limp mode but the MIL was still present on the dash. Drove the car up the road and it ran great. About 1/4 mile into the drive it went into limp mode again. Scanned the car and P1688 was still present. Oil can been seen in the omp lines. Looking for some ideas as to where to go from here or if anyone has experience with this code.

 

Idk if this would help, but this diagnostic output thread helped me a couple of times.
There's also a post with some screenshots of trouble codes, but I can't make them out on my phone.

https://www.rx8club.com/series-i-do-...utputs-155947/

 

This is most likely an OMP switch fault/short/ or simple adjustment needed.
There is a fair bit about it that lots of people far knowledgeabe then myself have posted on somwhere here.
Im also on my phone and cannot link you in currently. You should find it easily and yes its a bitch of a code!

 

I’m not sure which is worse; the guy who still hasn’t figured out how to search or the guy who can’t post a proper link

it’s probably the big black sensor switch on the outside cover that needs to be adjusted, there’s nothing in the service documentation on it, but well discussed on here plenty of times

or at least the first thread I opened in a P1668 search; that was the fix because if it’s not in the correct position then it will flag the pcm to trigger a limp mode. I reinstalled the original OMP on a newly rebuilt engine and it threw a limp mode. It changed the position that much just taking it on/off that it triggered it.

since you still had it after bolting on a supposedly good OMP, then that seems likely

good luck

edit: next time please search first before starting a new thread on an old topic, thank you.
.

 

Thank you guys for your responses.

Team, I did a search on it which led me this far. I did not see anything on adjusting the black sensor switch. I will search for that and proceed accordingly.

 

I fixed the link.
Software update added an extra step to the process I was not aware of.

https://www.rx8club.com/series-i-do-...utputs-155947/

 

it’s better to search by browser than on here by adding 「site:rx8club.com」

otherwise I tried, but couldn’t resist a 2-for-1-opportunity to be snarky
.

 

Im all good with snarky haha. Because you're right honestly. All too often we see threads posted about the same thing over and over and people really should search more. I'm a supermod on rx7club an I'm constantly weeding out threads that I see the same questions being asked in.

 

I replaced the oil metering pump with another one I had on the shelf and everything is fine with the car. Runs and drives amazing. Odd that a previously good working pump failed on the shelf. I learned a lot in this experience I'll tell you that. So for now, the problem seems to be solved. I will drive the car, weather permitting, and report back. I'm only at just under 40 miles with the new pump. I feel as though it will be fine however, but there's always that chance.

 

it sounds like you didn’t try adjusting the position sensor switch? Because just taking it on and off is enough to throw the position out of spec because theres enough slop in the mounting bolts/holes relocate is slightly different. That would also fit into it being fine when you took it off and then throwing a limp mode when installed again at a later date

 

I did try but the first bolt snapped instantly. I then removed it to work on it in it's entirety and noticed a small crack on the position sensor. I decided to replace the OMP with another one that I had on an engine that I'm putting in my Nordic Green 04 as it appeared to be in excellent condition. I installed it and it ran perfectly without making adjustments to the position sensor. I've logged 58 miles on the car since install and so far so good.

 

You should be right then with no DTC after that distance. When i was having the same issues i would get the DTC return anywhere from 0-3km so you are likely sorted. Good job!
Just be mindful of the 12 starts (without battery being disconnected between any of the starts) as i found out the PCM does a full OMP check this way. This car is cyborg smart and therefore hard work to learn the way around them! Cross your fingers. Also let us know here that all is still well after lucky number 12 start. 😀 I have spent way to long messing with mine. Just happy i got it soted in the end.

 

I'll keep you guys posted. I wasn't aware of the 12 start logic. It hasn't been 12 starts as of yet. I do drive it every day after work for about 5-8 miles. The only other issue I've had with the car is a sticking intake manifold tuning valve. I cleaned if from the top with the uim off but did not pull it out and clean it. I found that the linkage was rusty and causing some binding. I used some BG In-Force and worked the linkage and now its free. I checked the vacuum diaphragm for the tuning valve and it holds vacuum and operates the tuning valve when vacuum is applied.

 

hey, I’m interested in the prior OMP that you took off; have a need for one that doesn’t require it to be operational

 

Team. I hope you planning on doing some OMP testing or switch testing. Cant send you mine as it might take a while from Oz. I know you were not asking me though!
I did end up getting my dodgy switch to work and there was no codes for this or any at all when the engine let go. Honestly no idea if OMP was even operating properly at this time. Yes i premix also. Only know there was no code. Kept it as a funcional spare? just in case.
I got a much younger unit put on during rebuild with about half the km on it. Did insist on the 12 consecutive starts before handing over cash to ensure no issues with the newer OMP as it would cause limp mode if it fails initial self test or the more involved 12th start.

 

I can send it to you if you'd like. I don't have a need for it.

 

not doing any testing, but have a need for one that doesn’t require it to be useable

thanks, will pm you

 

So as it states theres no real fix to this but throw money at it and hope i am a licenced mechanic here in Canada my omp i ripped out today and noticed the servo on the backside the housing for it is all cracked so i am suspecting thats why i get a code and my question is is there a part number for just that piece

 

Posted on wrong thread somehow, ignore

 

Daz911 you likely need to source a second hand switch as I dont think they are sold new other than in a kit which is big dollars.
The switches are known to go bad or even just out of sdjustment that you have likely read.

 

Hi first time posting. Just bought a 6speed manual S1 RX8 (2005). A few days after buying it, went into limp mode. Showing P1688 fault. Cleared the fault and was able to drive for a few days. It's returned now and comes back after 5seconds of running each time and straight into limp mode. Have removed OMP connector and position sensor connector and thoroughly cleaned with electrical contact cleaner. The connector doesn't click together but it physically won't go any further. Removed the rubber water shield to double check as well. Reading voltage on harness side of connector, top & bottom middle are reading 12V and outside two on left and right are all 0-0.03V. My understanding is one of these should have been 5V for PCM voltage. Checked MAF and TPS and bought receiving 5V so it isn't PCM.

Next checked resistance on pump side connector. None of the bottom row gave any resistance. All 0 ohm. Connecting top left/right to top middle gave 30 ohm and top left to top right gave 50 ohm. Connecting top row to bottom row gave 0 ohm and similarly connecting bottom row to each other gave 0 ohm.

Pulled the harness up in engine bay to clean further (was oil residue on back side of connector). Used a full can of contact cleaner. Then noticed the 2 wires going to position sensor were frayed and exposed. They had kinda melted together. Thinking this was the issue cleaned the wires up tapped up the exposed wire and plugged back in. Still have an issue. Please help on next steps. Am thinking OMP internal circuit is gone because of the 0 ohm resistance but no 5 V is also suspect.

Position sensor wires stick together


Wiring arrangement. Bottom 3 as described are closest to camera.