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'09 LX, A/C dead, mech. shot it down to a bad ECU???

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skimask

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Discussion starter · #1 ·
Like the title says... Got an '09 Ody, LX, 120K miles. A/C went out last fall right before winter. I let it ride until this spring. Took it in for an overdue timing belt swap, belts in general, filters, plugs, etc.etc.etc. and had the guys take a look at the A/C fail.

Mech just called up and said he shot it down to a bad ECU. WTF? Really? All this stuff I've been reading about rotten stators in the clutch, and this guy comes up with a bad ECU?

Looking at $900+ for that. Not digging it.

(Side note...I just got my arm out of a cast 'cause I broke my wrist. I would've done all the hard work myself except when a guy shakes my formerly broken hand, it's like shaking a wet noodle...not a lot of strength there, practically none, hence the reason why I just spent ~$1700 for somebody else to do the work on this timing belt and other stuff).

Called up the local Honda dealer. The guy said he's never ordered an ECU for an A/C failure.

Any thoughts from the crowd?
 
Discussion starter · #3 ·
Ya, that's rougly what I got for a quote for those...compressor a fair bit higher though. But swapping those is a shot in the dark, and as far as I know, pressures are good, and I'm assuming if the guy was a decent tech, he bypassed the ecu to kick the compressor manually...if he was a decent tech that is. I've got zero reason to doubt the shop I took it to. They've treated me good for the past decade or so, but then again I've only been there for tire swaps. Everything else I've handled myself.
 
Discussion starter · #4 ·
Talked to the manager of the mechanic. Said that he troubleshot it down to a bad "transistor driver" in the PCM.
Now...I know exactly what that means, 'cause that's my job and my business...fixing electronic-able thingies. Question I've got is, does he know exactly what that means or is he "reading off a script" like most folks seem to do these days.
I'll be talking to him tomorrow to see if he even took pressure readings, checked the pressure switch, temp sensor, etc...

Found the wiring diagrams for the '09. Couldn't find them last time around when I was looking last fall.
Looks like I've gotta shoot for continuity from the A/C relay, contact #2 (F10 on the connector) thru the A/C comp clutch to ground. High ohms/open = burnt out clutch, bad wire; low ohms = either good clutch or possibly shorted wire.
Also probably want to swap the A/C relay and the blower motor relay for testing. Blower motor quits, bad relay. If the blower motor keeps running, got good relays but haven't ruled out the "bad transistor driver" either.
Put a fused +12v on the A/C relay contact #2 (or short across #1 and #2) with the engine running to see if I can get the clutch to at least kick.
If that works, I'll tap a wire into A/C relay contact #3 to provide a ground path for the A/C relay coil and see what happens there. If that works, then I'll be fairly sure I've got a problem with the PCM activating the A/C comp clutch relay.
Furthermore, go back to the PCM, contact A13 and check for good continuity between A13 and A/C relay #3.

Basic electrical troubleshooting...once a guy has a decent schematic to eyeball...

Bitchofit is, I got charged $105 for a basic A/C diagnostic. If I find something OTHER than a bad PCM and can prove it beyond a shadow, I gotta wonder if I go back and whine about it and possibly ruin a pretty decent shop relationship, or suck up the $105 or get it fixed otherwise...or maybe prove that it's NOT the PCM and have them fix whatever's wrong... meh...figure that out later...
 
Discussion starter · #5 ·
#6 ·
Trouble-shoooting any AC system, especially the electrical portion of it, is very challenging, even to the seasoned mechanics. So...

A bad PCM is almost unheard of.

Re AC Relay check, I wrote detail instructions on pages 7-8 in the thread below. Focus on post #116:
http://www.odyclub.com/forums/52-2005-2010-odyssey/93901-05-compressor-clutch-troubleshooting-7.html

To test the AC Clutch, get a jumper wire and jump between terminals that say "To AC Stator" + "Always Hot 12V". This basically sends 12V to the AC Clutch, bypassing all other components. If the AC Clutch engages, then the problem is likely bad relay:

Image


Now, if the Stator is fried, in theory you can replace only the Stator, but in my experience chasing the Stator etc., you are better off replacing the compressor and done it. Again all the details are in those threads. I blogged my long saga with the AC system in those threads.
 
Discussion starter · #7 ·
cnn said:
A bad PCM is almost unheard of.
Click to expand...
<big booming movie voice>

Until Now.......................

</big booming movie voice>

:D
Relay socket thru the stator coil, 10 ohms = good
Relay socket "always hot" = good
Relay socket "keyed hot" = good

Jumpered across Relay socket "hot" and stator with the engine running = stator kicks in and out whenever I put the wire in the hole.

Relay socket "controlled by dash A/C switch" -> should be more or less direct to ground with the dash A/C switch on... = does NOT

Pulled the most passenger side connector off the PCM (the "A" connector). Ohm'd from A13 to relay socket "controlled by dash A/C switch" = ohm's checked good.

Conclusion: Since the dash A/C control panel "talks" to the PCM via the CAN bus, and I don't have any other faults, I think I can assume that the mechanic is right in that the PCM's ground driver for this particular circuit is blown out and not providing a ground to the A/C compressor/stator relay when commanded to do so.

Any ideas if anybody has any pictures on the main PCM's circuit board? If I get some time this weekend, I'm going to pull mine out, crack it open and see if I can see anything repairable, or hackable for that matter. If there is a transistor in there that's blown and I can't find a suitable substitute, I'm going to hack one in there...'cause that's exactly what I do (see attached picture of one of my latest projects:) )
 

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#8 ·
Perhaps pull a PCM from local junk yard or ebay (about $60-$70 on ebay) for a test.

If you have a friend with a similar van and nice enough to let you swap PCM as a diagnostic test (label which is which 1st), this is another way to go.
 
Discussion starter · #9 ·
Nope, nobody with similar vans...besides that, as far as my reading tells me, my van won't even fire up with a different PCM unless I get it re-flashed with my VIN/keys/etc.

I'm about to open up the PCM now. Hope I find something obvious...
 
Discussion starter · #10 ·
Gave up (for now) trying to get the PCM apart to get the circuit board out.
Sealant all the way around the case itself, finally got that separated and exposed the back side of the PCB, broke off one tab where a screw goes to hold the case together, but it'll still go back together no problem with a bit of extra sealant there.
But still can't get the circuit board out of the aluminum housing due to all the sealant around the connectors themselves.
Ordered another PCM off ebay (37820-RGL-A01, same markings as mine except for the serial number). $45 there plus another ~$200 or so to get it reflashed/programmed at the local dealer. Assuming it works, ~$250 to get it done.

Aside from all that, I'm going to start another thread about the input conditions for cycling the compressor...temperature inputs, sensor inputs, etc.

As far as I can tell from the wiring diagrams, the only inputs that affect cycling the compressor are the evaporator temp sensor (http://techinfo.honda.com/rjanisis/...s/content/rjxa_isisviewer_ui.aspx?content=svg.svg&k=HH0810060004A_0001&p=EM&t=V) and the A/C pressure switch (http://techinfo.honda.com/rjanisis/...s/content/rjxa_isisviewer_ui.aspx?content=svg.svg&k=HH0810060005A_0001&p=EM&t=V).

If it's like every other car I've dealt with, the compressor kicks out when system voltage is too low, coolant temp is too high (or too low), outside air temp is too low, throttle is at WOT, and so on. If those are the cases, I just might try to whip up my own controller and bypass the PCM and A/C compressor relay...'cause that's just the kind of guy I am...
 
Discussion starter · #11 ·
Well, unless I got a 2nd PCM off ebay with exactly the same problem, looks like it's NOT the PCM. Really not that surprising...

Done so far...

Had a 'diagnostic' done by a local shop (not the local Honda dealer) which initially shot it down to a bad PCM. I'm assuming he really checked high and low side pressures, checked continuity in the pressure switch, etc. before shooting it down to the bad PCM. If it's one of those, I'm gonna go ballistic on 'em.

Manually jumped the relay contacts to make sure the compressor actually kicks in...which it does.

Got a good 12v at the relay contacts...can light up a fog light with it so I know I can draw at least 7 amps thru those contacts.

Got a good 12v at the relay coil contacts...can't light up a fog light but can kick the relay itself by manually wiring in a ground to the relay coil.

Swapped the A/C comp relay with the other 2 (fan relays). No fix.

Swapped PCM's (there's $200 down the drain for the re-flash :) ) No fix.

OBD scan doesn't show any CAN bus faults (necessary for the dash mount controls to talk to the PCM to enable the compressor relay, etc) or any other detectable faults.

Visually inspected the condenser, lines, etc. for the road damage. None noted.

Fuses all good.

Any other swell ideas?
It's only 60F here. I don't expect the compressor to kick in with A/C selected, but it should kick in with the defroster selected.
 
#12 ·
Have you or your mechanic done the most basic step: checking R134a pressure with AC Off?
If less than 80 psi when AC is Off, there is a leak.
Search forum for condenser gutter guard etc.
 
#13 ·
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Discussion starter · #14 ·
Condenser - chk'd for damage, etc. Good to go. Pressures good with compressor manually engaged and after it's been sitting for awhile. (I notice I forgot to mention that pressures had been checked good). Pressure switch also checks good with a load lamp.

Talked to the guy at the Honda dealer that flashed the PCM today. Said he's never seen anything this weird before. Usually it's been straight-forward...switch, compressor, stator, etc.etc.etc.

Then went down to the other shop and talked to the guy that did the initial troubleshooting down to the PCM. Sounded like he knew what he was doing. Troubleshot everything I would've done. Remembered details about the wiring diagram for the vehicle and the schematic for it. Came up with the suggestion that it's entirely possible that the relay socket itself is crap and/or cracked...the plastic of the fuse panel/relay panel itself.
Said he's seen it in a fair number of GM and Dodge vehicles where everything checks good until you throw a relay into the socket and put some stress on the plastic surrounding the sockets/etc and breaks the connection. I've shot the wires with a load lamp from the relay socket to the PCM. Good current, no appreciable resistance, etc. The cracked panel theory is a bit far fetched, but no farther fetched than 2 bad PCMs in a row.

The only other thing I can think of is bad CAN comm's between the dash A/C control panel and the PCM itself. But that 'should have' come up with some sort of CAN bus communication OBD error.

Whatever the problem is, the main thing is that the PCM isn't pulling that line to ground. I hate to tap into that A13 wire directly at the PCM and possibly break something else in the process, but if that's what I gotta do, then...there ya go...

With all that in mind, this weekend I'm going to whip up a relay-socket-extension type thing where I can probe all the pins with the relay "installed", attempt to figure it out. That should verify whether or not the actual fuse/relay panel base is good, bad, or what... Like I said, far fetched, but not out of the realm of possibilities.
 
Discussion starter · #15 ·
EE4Life said:
Check out these references for A/C troubleshooting:

See pages 3-7 of the August 2013 Honda Service News for this article:
Troubleshooting an Inoperative A/C
http://www.odyclub.com/forums/9-problems-concerns/41641-honda-service-news-7.html#post889482

See this Tech2Tech video:
amv120702
A/C Troubleshooting With the PGM-FI Data List
http://www.odyclub.com/forums/9-pro...lems-concerns/91553-honda-tech2tech-videos-service-technicians.html#post1038506
Click to expand...
I got a "Link Deny" with the second one, but that A13080 pdf file came up and has some good info. Thanks.
And I'll watch that video later...see if I can spot anything.
 
#16 ·
skimask said:
I got a "Link Deny" with the second one, but that A13080 pdf file came up and has some good info. Thanks.
And I'll watch that video later...see if I can spot anything.
Click to expand...
To avoid the "Link Deny" issue, see one of the newer model year TSB sticky threads for instructions.
 
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Discussion starter · #17 ·
Was unable to get the videos to open up, however, was able to look thru a few more of the schematics/etc at "http://techinfo.honda.com/rjanisis/content"

Correct me if I'm wrong...
Independent of the A/C compressor clutch circuit, when I select A/C or defrost, one of the radiator fans should come on???
I'm wondering if that's got some bearing on the issue at hand. Radiator or condenser fan cooling fan fails, PCM says no-go to the A/C compressor...which I would think would trip a fault, but.....

It hasn't been very warm up here, since last summer anyways, I don't do much in-city stop-and-go driving, and come to think of it, I don't think I've heard either of the radiator fans come on for quite awhile...at least since last fall.

The Ody has never overheated (that I know of), nor has the temp gauge gone up past 1/2, which is where it normally sits. So, I would assume either A) It hasn't gotten hot enough to do so, or B) the fans are working normally and they're quiet enough to where I can't hear them inside the vehicle.
 
Discussion starter · #19 ·
Yep, saw that schematic somewhere else, and read thru that thread. A lot of good info, but nothing that applies directly in this case. And, of course, doesn't tell you if the PCM is programmed to turn on the condenser fan whenever A/C (or defrost) is switched on or not. If the Ody is like my '95 & '98 Sentra and '05 Vibe, then, yes, at least one of the fans should kick in as soon as the A/C (or defrost) is turned on, no matter the outside temp. Mine doesn't, A/C or defrost, neither fan turns on. And again, not hot enough outside to kick in the radiator fan either....well, maybe if I let it sit and idle for an hour with the radiator covered up with cardboard, etc.
 
Discussion starter · #20 ·
Well... It's fixed! I'm happy...-ish... $210 for the fix at the local Honda dealer/service. No parts. In short, evac'd the system and recharged it twice, and it started working. Go figure...

Going in to talk to the guy that did the work 'cause the service sheet doesn't tell the whole story and I'll update here as needed tomorrow.

From the service sheet...(my comments in parenthesis)

- Checked A/C clutch and relays, all working (I did this as well).

- Checked pressure switch. Not working. (It was working when I checked it but I don't know if my '09 Ody has the On/Off type switch or the variable type that gives the PCM a relative pressure indication rather than a Go/No-Go input signal).

- Bypassed switch, A/C came on, but not getting cool. (It was getting cool when I hot-wired the clutch itself at the relay a few weeks ago).

- Checked A/C pressures. Found little to no pressure in either side. (Pressures were good when I took it to the original mechanic for the timing belt change last month).

- Evac'd system. System was empty. System would not hold vacuum. Added 1/2 pound (.22KG) refrig. Safety valve on compressor went off. Evac'd system again. Removed 3 pounds (1.3KG) of refrig. Placed system under vacuum. System held vacuum. Charged system to .75KG (1.65 pounds). A/C system operates normally.

--End description from service sheet--

Any good ideas what was going on here?
Almost sounds to me like something got plugged up somewhere and evacuating the system pulled whatever it was loose.
 
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