When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi first time posting. Just bought a 6speed manual S1 RX8 (2005). Just 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 OMP connector doesn't click together but it physically won't go any further together. 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 fault.
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 58 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.
I had a similar experience amd the same DTC and went through many of the diagnostic steps that you did and I eventually replaced the OMP and it solved the issue. I was lucky enough to have a known good OMP on the shelf and I used it as a diagnostic step and just left it installed after it fixed the issue. I did replace the OMP mounting and line crush washer when I replaced it to ensure there were no leaks.
Ok thanks for the advice. Hopefully don't have to replace the whole OMP due the cost of them new now. Do you know what is the procedure for resetting the pump and position sensor? I believe it's some combination of clockwise and anticlockwise 30° for the sensor but do we take the pump off to reset that?
