Code 21 - VTEC Solenoid Valve
 

A minor mystery I'm trying to resolve. I thought others might find interesting and have some suggestions.

Code 21 is regularly displayed, but will occasionally go off, but not for long.

Much earlier, the connector from vtec solenoid to harness was damaged; wire pulled out of connector on harness side. So I have a poor-boy connection rig between harness and solenoid. This has worked well for some time, until the Code 21 appeared recently.

"Poor-boy connection" - The harness side wire is pinched between connector guide post and electrical pin. Paper towel is jammed into connector to hold everything snug, and tape wraps the connector hold everthing snug.

I thought for sure the connection was the issue, but when I examined, I was doubtful, so I decided to check resistances of the solenoid.

At connector to vtec solenoid, ~14 ohms
At fender intermediate connection, ~14 ohms
At ECU connector checked and resistance was about 15 ohms.
Checked wiring resistance; from fender connector to ECU connector; showed low resistance.

Wiggling wires and tapping solenoid produced no changes.

The shop manual says solenoid resistance should be 14-30 ohms. I'm at the lower end of the range, but in the range. I also directly connected solenoid briefly to battery and heard click from solenoid.

After the above checks this morning, started car and CEL appeared immediately. Code check confirmed code 21.

Thoughts, suggestions?

regards

Pretty basic troubleshooting from honda. first thing i'd do is replace the harness connector and then recheck the ohm specs. if it's out of spec, replace the solenoid, if it's not then replace with known good ECU...i'm willing to be the valve is bad. you could also do the solenoid inspection, make sure the filter is not clogged up.

First thing I'd do is solder that wire connection together, just to eliminate the wedging, paper-towel, & tape. But that's juse because I have a soldering iron & can do that easily.

That's my plan, but I will probably crimp a new male/female connector in place to join the wire and recheck resistances.

I thought I could repair the harness side connector but that didn't work out and I never got a permanent replacement.

thanks

After driving yesterday w/ CEL on for first end of 50 mile trip, the CEL went off when I restarted for return and has remained off.

Today I removed the Vtec solenoid connector and spliced wire directly to engine harness wire w/ a crimp connection. Upon restart CEL remains off.

I'll drive to see if CEL comes back again. I suspect it will, but would be pleasantly surprised if it does not.

regards

I checked resistance at ECU connector today while moving harness, vtec solenoid wire, etc. No change at 14-15 ohms. Looks like ECU fault.

I tried my original ECU which I replaced due to a Code 9 fault that I traced to ECU. I thought the connector-circuit board jumper solder connections at the circuit board might be the problem and re-soldered them. Today I installed that board to see if problem was resolved. No, the same symptoms (missing, rough idle) and CEL on immediately.

So I swapped my board w/ the code 21 fault, which at least runs good, and started shopping for a replacement ECU.

I'll post if a replacement ECU resolves the issue.

regards

Are the tops of the capacitors flat on your ECU board, or are some starting to bulge a bit?

It seems like we are starting to see increased instances of ECUs going bad on the 94-97 accords.

I opened up and examined w/ magnifying glass and could not see any signs of distressed or damaged components. Hard to understand why a board would fail except solder jt fatigue damage. W/o a circuit board diagram it's hopeless to find a fault.

regards

I received a used ECU (matching 37820-POA-A51, $47 inc. shipping) and installed this morning.

CEL which had been on steady for several days immediately went off. So, looks like ECU was the problem. I'll post a final followup after a week of driving.

This is my 2nd failed ECU on this car. I formerlly though Honda ECU's were bullet-proof, but looks like age is beginning to take it's toll. Hope this is a good one. I see Reman units for $300, which may be a good option if they keep failing regularly.

I will open and do a post-mortem on mine but I'm not otimistic I'll be able to visually spot any faults.

regards

seems like refurbing these ECUs could be a decent side business for the next few years.