Code P0685, ECM/PCM Power Relay Control Circuit/Open?

Tiny
MJIMALI
  • MEMBER
  • 2010 HONDA CIVIC
  • 1.8L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 40,000 MILES
Hello, thank you for your time. I have no check engine light coming up but have experienced the following: sometimes the car won't start from first try; random irregular acceleration/hold up feel while driving; random engine shutdowns. I connected a scan tool and the code appeared as "pending" (nothing pending about the symptoms, though). This leads me to believe it can be a faulty ECM, rather than simple relay failure, etc. I just wanted an unbiased third opinion.
Sunday, November 6th, 2022 AT 6:58 AM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

Based on the description, it sounds like a failing fuel pump. Have you checked the fuel pressure to make sure it is within the manufacturer's specifications? Also, is there any dark smoke from the exhaust, odd smells, or anything other that you have noticed?

If the fuel pump is failing, the vehicle may or may not set a code because it thinks it's running out of fuel. The crankshaft position sensor does the same thing. If it is happening only when the engine is warmed up, that would be my first thought. If it happens regardless of engine temp, then I would start with fuel pressure.

Here is a link that explains in general how to check fuel pressure:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Also, the picture below provides the manufacturer's pressure specifications. Check this and let me know the results. If you have no pressure gauge, most parts stores will lend one to you.

Take care,

Joe

See pic below.
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Sunday, November 6th, 2022 AT 9:16 PM
Tiny
MJIMALI
  • MEMBER
  • 2 POSTS
Hello Jacob,

Thanks for your reply. We checked the fuel pump, and it seems like it's working properly. However, upon further testing, I've seen the car isn't properly showing codes (the P0685 appeared as "pending", sometimes not at all -- checked with different scanning tool -- had the green key blink once and disappear from the panel, etc.), Nor turning on the check engine light. Later the car refused to turn on; afterwards it turned off while running. I'm inclined to believe it could be the computer because it's giving misreading's or no readings at all, despite these symptoms. I'll be checking the computer, relays, connections, etc. To see if something comes up. That'll be the next step.

Thanks again for your help!
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Tuesday, November 15th, 2022 AT 1:31 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,101 POSTS
Hi,

Something strange is happening. By the way, thanks for the update.

Let me know what you find. Make sure the connection at the PCM is tight, clean, not damaged, and none of the pins are corroded or bent.

Take care,

Joe
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Tuesday, November 15th, 2022 AT 7:33 PM

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