A month or so ago got a DTC 8, "Top Dead Center Position (TDC) Sensor." Checked the plug by the timing belt cover and it was clean/nice and tight. Hoping for a one-off electrical fluke, reset the ECU and the CEL didn't come back.

Yesterday got a DTC 9, "No. 1 Cylinder Position (CYP) Sensor." Took off the cap & rotor. Everything was clean - not a trace of oil - and the connectors were all clean and tight.

Looked at the wiring diagram to see if there was a common connector in the engine compartment. Didn't think so since one sensor is behind the crankshaft pulley and the other's in the distributor. But I did notice that both sensors go to ECU plug C. Unbolted the ECU from the floor, pulled it back to look at it, and plugs C and D slipped out by themselves without pushing the release tabs. Plugs A and B were locked in place. Screwed around with C & D and found that they needed to be pushed pretty hard into the ECU before they were fully seated; seated so that they couldn't be pulled out without depressing the tabs. Took them back out, looked at the plugs' female pins and the ECU's male pins and saw nothing wrong.

Don't know if this is a fix or not but in the future I'll yank on the ECU plugs to make sure they're locked in with their tabs before bolting the ECU back in.

 

Thanks for the info. Let us know if the CEL returns. Hopefully it is fixed.

 

DTC 8 came back. Sensor resistance measured 336 Ω vs. min spec of 350 Ω per need help with trouble code 94 accord. Checked a junk yard distributor and it measured 340 Ω so I decided to leave everything as is. Took the car on a 1500 mile trip and the CEL didn't come back. I think I'll keep an eye on Craig's List for another P0H ECU. Wouldn't hurt to have an extra and it would be helpful for diagnosing oddball problems. I did run across a Honda TSB for Civics that blamed CYP sensor DTCs on excessive AC ripple (>0.5 VAC) from the alternator. Measured mine @ 0.1 VAC so unlikely that ripple is popping the CEL.

 

Correction on the post above: It was a DTC 8 that came back, but I went troubleshooting for a DTC 9. Dumb.

Anyway, after that 1500-mile rountrip and probably 30 on-off cycles with no CEL, today got a DTC 9, which is what I was troubleshooting in the previous post.

Somethin' funny going on: two unrelated CELs. Plus have an annoying alternator(?) "motorboating" noise coming through the tweeters after the audio install next month. Although 0.1 VAC is a good ripple measurement, that's measured with a DVM which I assume is an average AC voltage measurement, not peak-to-peak or RMS. So there could be high AC peaks even with low average AC.

I have the alternator from the F23 but it has a different plug than the F22's so I couldn't use it for the engine swap. Looking at a parts vendor's website I found the the brush holder and diode pack are the same part numbers for the two engines, so I'm going to try swapping them out. Only 116K on that F23 alternator.

 

Swapped out the diode pack and brush holder assy. from the F23 alternator to the F22 alternator. No CELs after a 15-mile round trip and six on/off cycles but that doesn't prove anything. I'll just have to wait and see. The F23's brushes were about twice as long as the F22's so there's at least some gain from the work. Cleaned up the slip rings with some 1000 grit emery paper while I was at it.

Perhaps unrelated, but for the past several months the SRS light's been popping on with SRS code 8-5, "Internal failure of SRS unit." Every reset results in the light staying off anywhere from two minutes to one month. The light's off now; maybe it will stay off? If so - and if the CELs stay off - then the "new" diode pack will be like a magic elixir: cures all that ails ya.

 

A bad diode can send voltage spikes around the system, which might give bogus problems that seem to be unrelated to the alternator. Hope it turns out to be fixed.

 

No joy. Yesterday DTC 9, "No. 1 Cylinder Position (CYP) Sensor" pops up.

CKP/CYP/TDC all have one thing in common: the shield wire:





Searching the ground distribution diagrams, found that the shield wires are spliced together and terminate at G114 "LEFT REAR OF ENGINE", but I'm using a wring diagram that's probably not for USDM cars. I think it should be G101 for my USDM. Also found that the shield wires connect to C452 "CENTER OF DASH". This problem cropped up after a radio R&R so I'm going to go looking for that connector. C452 also provides the ground for the Data Link connector so it should be easy to trace.

 

This right side interior connectors diagram is for earlier 5th gen Accords, there may be several differences for the later OBD-II Accords. However, junction connector c452 (connector has 20 cavities) should be under the right side of the dash.

 

Thanks, Redbull. Took the consoles out and measured those grounds and the grounds under the hood. Less than an ohm difference between them and the battery post. I guess the shield splice can be broken but I really don't want to tear the harness apart.

I have another shade tree theory. These CELs started popping up after an audio install. The tweeter amp is behind the radio and it's a real piece of crap: a Pyramid. Noisy, lots of alternator & engine noise, even with the RCA and power cables properly routed and a coil/cap commercial line noise filter on its power input. I'm guessing that amp is spraying EMI and, since it's really close to the harness the carries the sensor and shield wires, then it may be triggering those unrelated CELs. Removed the power from that amp and I'll give it another go. If it fixes the problem then I'll dump the amp and go passive on the tweets using the HU's high-level outputs and a couple of caps.

 

No joy after dumping the amp. In cold weather DTC 9 pops up fairly frequently, every week or even every day. In warmer weather it pops up anywhere from two weeks to two months. No engine running problems whatsoever.

Bit the bullet and bought a used distributor and coil for $30 and swapped out the dizzy today. Emissions testing is due this month so I hope DTC 9 doesn't rear its ugly head before then, or ever again.

Measured CYPP - CYPM resistance 365Ω on the old dizzy, 370Ω on the new dizzy, vs. 350Ω min / 700Ω max spec. I'm hoping that there was some temperature-induced flakiness in the old dizzy that the new dizzy will fix. If the problem comes back I'm going to have to drag out my scope to look at waveforms:

motor(dot)com/magazine/pdfs/052011_04(dot)pdf

ozhonda(dot)com/forum/showthread.php?67843-DIY-PGMFI-Diagnostics-Code-9-CYP