I’m buying steak dinner for the guy who gets this sorted out!

I will try to be relatively succinct. My elevator pitch is that this 2003 Accord seems to have some sort of electrical issue which may be causing failure of the PCM. I sure could use some help on this one!

OK, here what we’ve got:
2003 Accord 2.4L i4 EX Vtec Coupe (Gen7) Auto Trans.

I am a mechanical engineer and one of my dad’s electrical engineering friends is helping with this one too. Additionally, my wife’s second cousin owns a small repair shop. We have any and all (non Honda-specific) tools at our disposal (scope, meters, scan tools, etc.)

Background of car & issues: The car has, since my dad bought it at 60,000 miles in 6/09, gotten fairly poor mileage (low to mid 20s). I can squeeze a TL to get 30-40MPG and was unable to break 30 mpg in the Accord when I was anticipating 40+. This may be a bogey. Anyway, downstream Air/fuel ratio (AFR) sensor (some mistakenly call it an O2 sensor) was replaced @ 85k in 2011. Replaced air filter and spark plugs @ 105k in early May 2014 to try and improve mileage.

A few weeks later dad started noticing “transmission issues”. While driving CEL intermittently came on, RDNL lights on dash gave a light show. Then, in the same trip the green Neutral LED indicator would intermittently illuminate. When illuminated with constant throttle, engine speed would drop to ~700 RPM. Once LED was off, car seemed to drive properly. He also reported that once he got home it felt like tranny was slipping.

I bought a scan tool for use with my phone and it indicated the tranny switch (aka RDNL switch) was faulty (among a few other faults which I thought might have somehow been caused by this main fault). I also want to note that in playing with my new scan tool, I found it strangely odd that I was unable to graph the downstream AFR sensor from the OBDII port. Anyway, I replaced the switch. The problem returned. He took it to the wife’s second cousin auto shop guy and I don’t think he was able to see any CEL or symptoms at that time. He referred us to a tranny guy that specializes in Hondas. He too didn’t observe any issues on his test drive. He said he could pull it to clean the screen and flush, but very well may not fix issue. (some of this paragraph may be out of order as my memory is a bit fuzzy here).

One of the times dad called in a panic, he said he was driving at constant speed when, suddenly, billowing blue smoke came out rear of vehicle. I confirmed, “Blue smoke? Like, definitely not black fuel, but blue as in oil?... After warmed up and at constant velocity?!”. “Yes, definitely blue smoke.” The only possibly explanation I could come up with was EGR or possibly VTEC although I would think latter would be under load with increasing engine speed.

I started thinking about those other faults and we called another mechanic friend of my father. After fessing up that we had some other codes and talking through them. He was fairly confident that there was never anything wrong with the tranny and that there was probably some electrical issue. I immediately slapped myself in the face and started taking detailed notes of the rest of the conversation. In summary, he said that we ought to probe around and see if an AFR sensor is bleeding back to PCM or maybe we have a bad ground… check relays, fuses, etc. So we did. I probed A/F sensors and didn’t really think I had an issue, but I wouldn’t bet much that I knew what I was looking for/at. I can share that data. Some of the CEL codes we saw: P0138 (B1S2 O2 sensor circuit high voltage), P0107 (MAP circuit low input), P0122 Throttle/Pedal Position Sensor circuit low input). There were more intermittent ones, but I need to go back and verify order of events before leading you all astray. Those were the codes I discussed with him and he came up with a story that could explain them all. We found the G101 ground from intake manifold to chassis, took it apart, sanded and reinstalled it (although it seemed fine). All fuses were/are good. All relays in engine compartment seem happy – we can feel them clicking over and we removed most or all of them and re-seated them.

Then, one day dad tried to move the car. He backed it out into the street and it died. He was unable to shift out of Reverse to get it out of the street. I talked him through using the manual release near the shifter and he pushed it back into the driveway. The car would not run. Once I got there and diagnosed for a while I realized that the Immobilizer Unit was unhappy (continuously flashing green key indicator on dash with ignition on). It was at this time when I decided the PCM has got to be fried. We pulled it and could not believe what we saw. There was an egregious amount of aluminum oxide all over the inside, corrosion of solder joints and PCB components galore, and several charred/black spots on MOLEX pin connectors to board. Remind me to upload pics! (I found some other forum posts that evap coil is above non-sealed PCM and some Honda engineer has hopefully been hanged… last words are mine, not from forum). Anyway, I found a pin-out diagram of ECU and cross referenced the bad spots… sure enough one was to G101, one was to EGR valve, and another was for “PGM-Fi main relay 1” which I believe drives the Immobilizer system . Check, Check, and Check – we’ve got a smoking gun. Problem is, we knew that a failed PCM could be a cause or a symptom of an upstream problem. We cleaned the contacts within the PCM and mating connectors as well as tried to find any broken solder joints (which we did not) and plugged it back in. We actually did get the car to run for about a minute, but it was not enough time for me to complete the OBDII scan.

Anyway, we got a replacement PCM from junkyard (was actually for a 4-door with slightly different part number). We towed vehicle to Honda and had them reflash PCM #2 with VIN & Key Fob. For reasons I can’t seem to recall, we replaced the front AFR sensor. Car started and seemed happy. I left him my scanner and installed the reader app on his phone. We told ourselves that we/he would scan the car regularly with or without CELs and try to make sure if something pushed the PCM over the edge (instead of internal corrosion over time from water ingress), we’d do our due diligence to find it. You see where this is going, right?! We also said that we’d find some sort of plastic bag or wrap to further isolate the PCM from any dripping water.

Dad drove it around the block a couple times and then on one highway trip – maybe 30 miles total. The gremlins are back. He had strange tranny issues with it shifting. The engine light was on. He came to a stop sign and the engine died. After a few minutes, it started and he was able to limp it home. He said it ran roughly for the first 15 miles and then seemed ok. He got home and turned it off and on a couple times and went from drive to reverse without any further issues. Just to make it a good puzzle, he did not ever run the scanner. He parked it and then late at night the alarm sounded. He could not make it stop so he pulled the battery. Goodbye trouble codes.

That pretty much brings us to today. I went over there the other day and pulled PCM #2. Inside looked 1000 times better than original one – I saw no obvious damage, but there was some aluminum oxide which I presume was from its previous life. This assembled PCB seemed to be coated in a thin epoxy-type sealant – nice band-aid Honda.

I pulled downstream AFR sensor, which, I am speculating may be the/a root cause. Dad’s electrical engineering friend said he’ll break down the original PCM and see about reviving it before we order PCM #3 and tow the vehicle back to dealer. I assume that either PCM 1 or 2 could theoretically run the vehicle since they are both programmed with same Key and VIN, right? I’m speculating the non-original downstream AFR sensor may not be OEM and, therefore, may be a simpler O2 (only) sensor which I did read on a couple forum posts is a no-no on late-model Hondas – and might also help explain poor mileage (although I'm not sure why it hasn't been throwing codes).

So, I guess my question is, am I seeing the forest for its trees? Anything obvious that I’m missing sticking out to you guys? Any help would be greatly appreciated. Believe it or not, I glossed over some details in hopes that I could keep at least a couple folks’ attention span for my diatribe to get this far. I was thinking that if we could get a happy PCM and run the car without issue (with downstream AFR sensor unplugged) we just replace it for ~$70 and move on with our lives!

 

I think that you need to take a step back and start the diagnosis over.

I would disconnect the battery and clean all ends of both battery cables with a wire brush or sandpaper. Drive the car and use the scanner to record any codes. Post them on here.

You may also want to hook up your volt meter to the battery and verify the voltage is around 14 volts with the engine running.

I would also suggest monitoring your fuel trims when driving and/or the A/F sensor.

 

Thanks for the response!

Currently, the engine will not run. The Immobilizer (green key icon) is flashing and does not allow engine to run or OBDII communication with scanner. Perhaps, I should go back through communications and gather any data that may have been overlooked.

We did put a fresh charge on the battery as well as cleaned battery posts and collar clamps with wire brush and sandpaper. We properly fastened M10 post bolts to provide a secure connection.

Today, dad's friend brought PCM #1 back after inspecting and cleaning and, unfortunately, was unable to get Fonda to fire. He noted that there were some flashover points on the rear of the PCB we could not see before disassembling it. He noted that the original PCM did have a (worn) coating over PCB assembly as well. He took PCM #2 home with him to inspect and hopefully find a failure on it he could fix.

If PCM #2 is fried, I'm tempted to order PCM #3 from car-part.com, unplug as many things from car as possible to still allow to run, tow to dealer to reflash PCM and then very carefully start plugging things back in saving rear AFR sensor for last.

 

For the current issues of it not starting & unable to get a OBD-II reading, check under-dash Fuse No. 19 (15A) to make sure it is not blown. Fuse No. 19 protects the ECM/PCM, Immobilizer control unit-receiver, and PGM-FI main relay 2.

 

OK, we checked fuse 19 (and swapped with another for good measure) - it is ok. We also pulled the kick panel and checked some of those relays as well (found PGM-FI Main instead of PGM-FI Main 2). For what it's worth, it seemed as if only the relay labeled "P/W" was activating upon Keying-on to ignition. We pulled all 7 relays in the board and measured coils as we expected around 100 Ohm.

We topped off the battery with a charge and then ran another wire from Intake Manifold to Battery negative post just to triple check that ground.

PCM #2 has been disassembled, inspected for obviously failed components, cleaned and re-installed without success.

We called dad's mechanic friend buddy (who does not normally work on Honda's but is incredibly knowledgeable), he said that the vehicle may have a "body module" which would work in conjunction with PCM and would likeley include safety equipment such as airbags and that it is possible that this may not be happy. I pulled the cubby under radio and found the SRS module, but left it alone.

During this call dad reminded me of something that never sank in the first time. He said that when he drove the vehicle immediately after re-flashing with PCM #2 each time he started the car he got a 10-count flash with the maintenance required light. The mechanic said he has had issues with an improper part number PCM giving a similar error. We were considering the possiblity that the PCM may electrically be fine, but may have lost it's flash.

Also, EE friend read that Honda's have some sort of Immobilizer over-ride that is supposed to give some amount of time to drive the car (presumable to a dealer). I found this link that sounds like it (for a Prelude), but it doesn't exactly explain how to do it. I'm considering calling dealer to inquire so we could get out of renting the toe dolly again.

Immobilizer Bypass? - Honda-Tech


So, at this point, one way or another, we're planning on taking car back to the dealer for him to troubleshoot PCM #2 and see if it lost it's flash, if it's functional, etc. I'm tempted to just go ahead and order PCM 3 and bring it as well since a) PCM 2 is the wrong part number and b) it costs only ~$60 for a used PCM and ~$160 to get the car to the dealer and have them flash it. I guess our thinking is that it's time to stop guessing and try to make friends with a service tech interested in a good puzzle. I think we just need to capture his interest and tell him the whole saga.

 

Here is a photo of PCM #1. I took a bunch more, but cannot find them right now.


I've also uploaded a summarized PCM pinout since it wasn't as easy to find as I had anticipated. I found this from someone doing a KPRO ECU mod. This seems to be for the vtec i4 k24a4 engine, I believe it says in there that it is used for manual or auto tranny.
(PCM pinout summarized.pdf

Here is original link to full page:
How To: Install KPRO on your 03-05 k24a4 Accord - Honda-Tech

 

1. The immobilizer system comprises of the keys, immobilizer system indicator, immobilizer control-unit receiver, and engine control module(ECM)/powertrain control module (PCM).

You can read more about the Immobilizer system for your car in this service bulletin:
http://www.tegger.com/hondafaq/tsb/accord/x02-053e.pdf

2. The Immobilizer brake code is a 5 digit numeric code that is enter by using sequences of moves with the ignition switch and parking brake. The brake code is obtained from the dealer.

The following is generally the procedure and must be done correctly and within the allotted time.

1. Use an appropriate key blank and a suitable key cutter to cut a temporary ignition key. Refer to the special tools catalog for available cutting machines.

2. Release the parking brake.

3. Insert the temporary key into the ignition switch.

4. Turn the ignition switch to ON (II), and wait for the brake system indicator bulb check to complete.

5. Enter the first digit of the Immobilizer Brake Code by setting and releasing the parking brake that number of times within 30 seconds. For example, if the first digit is four, set and release the parking brake four times.

6. Turn the ignition switch to LOCK (0). (This enters the digit into the ECM/PCM.)

7. Turn the ignition switch to ON (II), set and release the parking brake the appropriate number of times, and turn the ignition switch to LOCK (0) to enter the second, third, fourth, and fifth digits.

NOTE: When you turn the ignition switch to ON (II), the immobilizer system indicator does not blink but stays on. The immobilizer system indicator stays on even when the ignition switch is turned to LOCK (0).

8. After you enter the fifth digit and turn the ignition switch to LOCK (0), the immobilizer system indicator blinks three times and then goes off. You can now start the engine with the temporary key.

NOTE: This procedure is only a temporary fix.

When you start the engine with the temporary key, the immobilizer system indicator comes on and stays on while the engine is running. Also, when you turn the ignition switch to LOCK (0), the indicator does not blink five times as it normally would.

9. Start the engine within 10 minutes or you must repeat this procedure entirely.

 

IT'S ALIVE!! Fonda lives.

Thanks for the help. We didn't piddle with coding a temp key since I didn't think it would save effort or cost in this case.

We towed her to the dealer with PCMs 1,2, and 3 last week. They were unable to communicate with #2 and said it seemed dead. They had no issues to program #3 (so far same story as previous trips with #s 1 & 2).

They purportedly had to plug in all sensors in order to run the PCM learn procedure which was not done with PCM2 btw. We had them leave the hot PCM laying elevated on the passenger floor board. They weren't too interested in helping us determine root cause of failure(s), but did agree it was quite possibly a clogged evaporator condensate drain line.

Once we got it home I followed the suggestions of these guys A/C Condensation Drains Into Cabin - Drive Accord Honda Forums. I could not find any obstructions in the condensate drain tube but blew plenty of seemingly unobstructed air through it. I didn't come up with an easy way to pour water in the pan to ensure proper drainage - anyone have thoughts there? I observed and felt all around the two-part evaporator box and could not find evidence of a leak path. Is it hard to take apart?

For good measure, we blew air through and poured water down each of the four sunroof drain lines and saw it immediately come out where we expected and not where we didn't. We also poured a good amount of water on the windshield and saw good drainage to the same two areas behind both front wheels and a dry PCM cavity under the dash.

So, for the first week I had told him to not run AC and just make sure it remained happy and scan for codes during at the end of every trip which has to date after maybe 60 or 80 total miles been clear of any codes.

Yesterday, I told him to go ahead and fire up the AC and to check the still empty PCM cavity for dampness (PCM is still in an elevated padded bundle on passenger floor). No word yet. When we fix or verify lack of water in that area we are planning on sealing cracks and gaps of PCM with silicone and then placing in reclosable gallon bag - any thoughts on that logic? My rationale is that many PCMs are in fact water-tight and installed in very unforgiving engine bays. Also, I figure it probably doesn't create much heat and even if it does, the gallon bag should not really be too much thermal resistance.

The only real issue has been that he's getting some sort of intermittent SRS/airbag light which I don't really understand because isn't the SRS pretty much handled in its own module and then just pass trouble codes through PCM? I did monkey with the three or so plugs when trying to diagnose the Immobilizer issue a while back. I haven't yet witnessed it. He says it doesn't throw a code on the OBD2 scanner for pending or stored faults.

Thanks again!
James

 

Not all OBD-II readers/scanners are capable of reading Honda SRS codes.

 

Regarding the Immobilizer brake code instructions, you only need a temporary key if you lost your key.