My car has been on and off having problems getting started when I turn the key. The check engine light recently went on and it says "P0689 ECM/PCM Power Relay Sense Circuit Low" or "P0690 ECM/PCM Power Relay Sense Circuit High" , the reason I'm not sure if it's either voltage high or low is because the technician messed up the reading and accidentally deleted the reading also reset my engine light. It sometimes doesn't start while other times it starts just fine. Do you know what could be wrong with the car if it says something about ECM/PCM Power Relay Sense Circuit voltage? Thanks!

 

You didn't say which model year. On the ones from the '90s anyway the main relay (aka PCM Power Relay) is infamous for causing "It cranks but won't start, but only sometimes". The soldered connections inside the relay crack and become intermittent.

 

Like mk378 said I would try swaping out the relay for the ecu. There should be a fuse panel (Black box) in the engine bay, open her up and follow the layout printed on the bottom of the cover. If it is not that, check all your connections for that circuit...XD

 

What year Civic? I couldn't find code P0690 or P0689 for Civics.

Take the car to AutoZone where they will retrieve the trouble code free of charge.

When the engine won't start, can you hear the low humming sound of the fuel pump priming for a few seconds in the rear (fuel tank area) when the ignition key is turned to ON without cranking the engine? If you do hear the priming noise, then your main relay is probably fine, so look elsewhere (e.g., retrieve CEL trouble code and troubleshoot it).

 

It is a 98 Honda Civic LX automatic 4-DR. It starts most of the time but 1/5 of the time it has good trouble getting started, I have to turn the key for like 4-5 times until it starts. This doesn't happen all the time but when it does it's frustrating. It sounds normal turning the key, it just wouldn't start --you know when after that turning key sound for two seconds the car stars to vibrate a tiny bit which is the engine starting, the car doesn't "vibrate" or produce any humming sound, just nothing after stop turning the key. This happens most often right after I used the car, then say 10 minutes later try to restart it, it would have trouble. But if i wait for like 2 hours or a day or two then use the car again, it acts just fine.

Is this going to be a major fix? How much would it cost assuming $50-60 / hour labor. Is this the "PCM Power Relay" the name of the part to check the price for a new replacement? Thanks!

 

As mk mentioned, it sounds like a classic case of a bad main relay; however, there are additional possible causes for an intermittent no-start problem.

Start here with the troubleshooting:
Does the CEL stay ON when the ignition key is turned ON without cranking the engine or when the engine is running? If so, retrieve the CEL trouble code(s) from the ECU as described at the link in my signature. Post codes in this thread for more feedback.