I hear what you are saying on the PCM but there are other issues that can arise from swapping i.e. keys don't work, immobilizer problems....

I have tried getting it to reset by disconnecting the battery for quite a while to no avail. What formal procedure is available to get the PCM to reset? I read somewhere that you can jumper the honda diagnostic port and prompt the odometer to return trouble codes, wondering if there is any method to force a reset. I have a OBD tool but nothing that does the honda specific ports.

I am quite sure the PCM if damaged can be repaired with relative ease by a qualified circuit board tech if the location of the grounding transistor is known.

 

Yes, you're in a tough position w/ no straightforward way out.

There are PCM repair services, and total cost might be less to repair than to replace and re-learn keys. However, it may be difficult to ID the correct transistor w/o a circuit board diagram. Only way is to trace from pin A27.

Some have had good results w/ the HDS clones. Searc "honda HDM clone" on google.

good luck

 

Thread is getting long, so I'm not sure if you tried this.

Pin #3 is a red wire going from the relay to the PCM. It plugs in the PCM at pin A27. You may want to back-probe that pin and verify you have no ground at the PCM when the a/c is turned on. This would rule out a bad wire from the relay to the PCM.

 

I got brave and pulled the ECU and disassembled it, the board is glued into the metal enclosure which makes it hell to get out without damage. I am a complete novice at anything circuit board related so I had a hard time tracking pin 27. I was able to track it to 3 separate transistors and all 3 tested as within range that they should behave normal based on ohms. Knowing that I was well out over my skis I decided to put it back in until I can find someone who can really isolate the problem...if there is one. Later today I will probe the red lead from the ECU and see what I find there.

Lastly, I noticed 2 additional relays under the dash, not sure what these relate to but I dont recall having seen them in the diagram.

 

There are lots of relays in a modern vehicle.

About all you can do is backprobe pin 27 and check for ground signal w/ AC commanded On. If that is missing, then another problem must be present. If present, then PCM looks to be problem.

Let us know your final resolution.

good luck

 

Just want to confirm, to bypass the pressure switch as the potential cause I need to ground pins 1&4? I mistakenly grounded pin 3 on the pressure switch connector and it kicked the condenser fan up to a higher speed consistent with what I am used to hearing on my 08 when the compressor cycles on.

 

You don't ground pins 1 & 4, you short the connector pins to each other w/ wire jumper to simulate closed pressure switch.

You can also check the 1 & 4 pins on the pressure switch body, which should show a shorted condition. If not, you've found the problem.

good luck

 

Got it, I had previously tested the pressure sensor in that manner and got continuity between 1&4 so i'm not holding my breath. The behavior of pin 3 is odd given what you have outlined

 

Probed 27 at back of ECU and found no ground, unless there is another input causing the problem i'd say that confirms its the ECU. It measured 60 ohms resistance to ground, with the relay in place probing the wire caused the AC clutch to engage. I'm gonna see if I can find anyone local who repairs circuit boards, this should be a simple task for someone who knows what they are doing.

 

Higher cooling fan speed is likely triggered by pressure switch B to increase cooling as compressor pressures increase above 213 psi.

good luck