CEL 9, Cylinder Position Sensor Check Engine Light

Tiny
SMCMULLIN33
  • MEMBER
  • 1990 HONDA PRELUDE
  • 2.1L
  • 4 CYL
  • MANUAL
I have a 1990 Honda Prelude Si with a B21A1 engine. I recently had the engine light come on and it is showing 9 flashes, or the Cylinder Position Sensor. I have checked the resistance of the sensor and it came back within specs, according to the Factory Service Manual. I have run all diagnostic procedures according to the FSM, checking resistance of the sensor directly at the sensor and at the end of the wiring at the ECU, all checked out within specs. I have tried a different sensor and also a different ECU, and the CEL is still coming up. I have checked to make sure that the crank to cam timing is set correctly. The engine was recently rebuilt and all was running fine, the only work I had done right before the light came on was replaced the alternator. I got my hands on a test harness and found that there is continuity when checking the wiring at the ecu test harness like the manual say, now my issue is a ran new wiring and the continuity and problems are still there. Why do I still have continuity at the body when testing at the harness and not at the sensor itself. This tells me it should be wiring but I replaced both wires and now change. Thank you for anyone who can help me.
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Friday, June 13th, 2014 AT 9:14 PM

15 Replies

Tiny
SMCMULLIN33
  • MEMBER
I missed the part about not plugging test harness into the ecu, there is no continuity but the cel is still coming on. Im lost and don't want to just throw parts at this thing.
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Friday, June 13th, 2014 AT 10:00 PM
Tiny
KHLOW2008
  • EXPERT
Seems weird that the CEL is coming on even when wiring and sensors have been replaced. At the thermostat housing, check and ensure the ground circuit is clean and secure.

What are the resistance for the original sensor and the replacement sensor?
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Saturday, June 14th, 2014 AT 10:59 AM
Tiny
SMCMULLIN33
  • MEMBER
955 and 946. I've already checked and cleaned this ground.
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Saturday, June 14th, 2014 AT 11:36 AM
Tiny
SMCMULLIN33
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Any other advice?
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Sunday, June 15th, 2014 AT 1:30 AM
Tiny
KHLOW2008
  • EXPERT
Does the CEL come on immediately or after some running of the engine?
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Monday, June 16th, 2014 AT 8:21 AM
Tiny
SMCMULLIN33
  • MEMBER
Comes on after about 5-10 seconds.
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Monday, June 16th, 2014 AT 11:38 AM
Tiny
KHLOW2008
  • EXPERT
Sorry for the delay in replying. Is the replacement sensor new or used?
You mentioned checking the camshaft timing, how sure are you that both camshafts are timed correctly?
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Thursday, June 26th, 2014 AT 11:27 AM
Tiny
SMCMULLIN33
  • MEMBER
I re did the timing as it was a tooth off, it's correct now. The sensor I'm using is used, the part is no longer available new. But both sensors test correct.
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Thursday, June 26th, 2014 AT 11:33 AM
Tiny
KHLOW2008
  • EXPERT
After redoing the timing, the problem is still there?
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Thursday, June 26th, 2014 AT 11:44 AM
Tiny
SMCMULLIN33
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Yes
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Thursday, June 26th, 2014 AT 11:51 AM
Tiny
KHLOW2008
  • EXPERT
Did you open the sensor cap to check if there are any contamination internally?
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Thursday, June 26th, 2014 AT 12:42 PM
Tiny
SMCMULLIN33
  • MEMBER
Yes I did, it is clean and rust free inside and both wires look good. I'm curious, could the distributor cause this on this motor at all? I know the sensors in the distributor help to sync with the CPS.
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Thursday, June 26th, 2014 AT 12:54 PM
Tiny
KHLOW2008
  • EXPERT
It is possible the distributor is related. Did you test/check the other 2 sensors? Distributor would normally throw a Code 4 or 8
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Thursday, June 26th, 2014 AT 1:41 PM
Tiny
SMCMULLIN33
  • MEMBER
I did but the distributor looks bad inside, both sensors did test good though. It is only throwing a code 9.
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Thursday, June 26th, 2014 AT 1:45 PM
Tiny
KHLOW2008
  • EXPERT
Sorry for not being able to help you. I have gone through everything and could not find anything that I could add in based on what you have done. Hope you can get the problem resolved. Good luck.
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Thursday, July 17th, 2014 AT 6:50 AM

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