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2002 Civic LX, A/T, 112k miles. I think the ECM died.
I get a call from my wife saying her car is acting weird. Temp gauge dropped to C suddenly in 90°+ F temps, rough idle, no power. I get to her to find I can’t pull OBD codes due to a “Failed Linking” error. We end up getting her towed home.
I diagnose the car at home, then researched here for similar symptoms to find that the most likely reason is a failed ECM. Here is what I see:
Diagnostic Observations
Check Engine Light (always on)
Blinking Green Key (even with engine running)
No Temp Gauge
No Tach when running
Failed OBD linking. No readings.
Idles with rich smell (limp mode)
Idle surges cyclically (no clicking relay) at first, smooths out somewhat about a minute after startup
Total lack of power in Drive
15A ECU fuse under hood is good
80A mega fuse for battery is good
I’ve read here to check the alternator for a good, tight mounting, which mostly check out...but I’ll delve in deeper to check this weekend. The alt is a replacement, not OE, and has been in service for approx. 14k miles ago during the 100k mile service (cam timing belt, water pump, etc.). As I said, I’m going to check for tightness and will clean between metal surfaces for a good ground this weekend. Electrically, here is how the alt tested:
Alternator Readings (POS multi tester lead to Alt + terminal
14.38 ~ .40V - grounding to Alt Casing (pretty constant reading)
14.11 ~ .14V - grounding at alt. tensioning wing-nut
0 V - grounding at engine-side Alt mount bracket (??? weird)
13.85 ~ .95V - batt Negative post
13.85 ~ .95V - grounding via engine ground strap to body
13.85 ~ .95V - grounding to a valve cover bolt
All that said... it feels like a fried ECU to me. If I find a used unit and do the swap, what exactly do I need Honda Tech to do? Does the ECU need a handshake/initialization to engine with VIN or is the issue just for key codings? There is reference here about using a car locksmith service. Can I get away with just that or do I need Honda Tech service for more?
Thoughts and opinions are appreciated.
Last edited by michaelj; Jul 16, 2020 at 07:51 PM.
Thank you very much, sdaidoji and BrotatoChip for the replies.
@sdaidoji - The info confirming *just* the need of key programming is excellent news. I live in a DC, so there's GOT to be some locksmith to do the work around here. We're gonna call around to be sure first, and to check to see what the price difference is for on-call, doorstep appointments.
@BrotatoChip - It hurts my heart to hear that, because it's confirmation that this is essentially my fault at the end of the day. I had replaced the alternator due to a seized and snapped off (+) terminal lug when I did the 100k big service. The alt is an aftermarket replacement. I'm hoping that THAT isn't also a potential issue. I do NOT want to do this all over again at a later date. I still have the OE alt with the snapped lug. I could potentially repair the lug and put the OE alt back into service. The car had to be back in use immediately at the time of the 100k service, so I went the most expedient route then.
Also, I'm going to make a junkyard run tomorrow to see if I can score a replacement ECU
Yeah, man. I absolutely hear you on about fixing the root cause before installing the swapped ECU. It's funny... cause I was just reading your reply about body grounds to check at this thread: ECU Fried?
I will do more checking to be sure about I'm covered on the root cause. As I said... I do NOT want to do this again!
It hurts my heart to hear that, because it's confirmation that this is essentially my fault at the end of the day.
Definitely a common thing we see. People get the top alternator bolt in, loose fit the bottom bolt, put the belt on and tighten with the wingnut, then forget to go back down and tighten the bolt and nut on the bottom. I've never done it (to my knowledge) but I've seen it on a friend's. Looked like the A/C compressor was replaced and alternator wasn't tightened afterwards. Somehow showed no symptoms, just stumbled upon it while doing the head gasket and timing belt.
As Ezone said, check it before installing a replacement ECU or you'll do damage to the replacement as well. There's always a chance yours is still okay too.
Definitely a common thing we see. People get the top alternator bolt in, loose fit the bottom bolt, put the belt on and tighten with the wingnut, then forget to go back down and tighten the bolt and nut on the bottom.
If the bottom bolt is the one that's really hard to access because the belt is in the way... than I remember that bolt!!! He's a jerk! But I'm moderately confident that he was tightened... though ego aside, I WILL check it. Also, if that is the bolt I'm thinking of, I was getting 0v at the engine-side mounting bracket of its position when I did my alt voltage tests (which is very very VERY weird to be as I was seeing voltage at other engine grounding positions: valve cover bolt, engine to body ground wire.)
Instead of an "Alternator Mounting Check" day as originally planned, it became a stomp around the junkyard for a couple of hours. This was done because today's temps are going to be in the low 90s and less-humid here. Tomorrow will be in the upper 90s, near 100! So we did the junkyard stomp early in the morning while it's as cool as possible. Incredibly, my wife likes junkyard runs, so she was an active participant in helping to fix her car.
We found a few M/T cars (one matching 2002 LX but failing due to M/T) and three examples of A/T cars: 2001 LX, 2002 EX, and 2001 EX. Facing the dilemma of a non-exact match we sat down in the shade to do some research. What I discovered is that anything from 2001-03 will work AS LONG as the donor matches engine and transmission specs precisely. Further research into the differences revealed that LX engines have lower compression, so our choice made itself at that point... the 2001 LX A/T gave us its brain. The three cars ended up being excellent practice vehicles for getting the ECM out with minimal difficulty.
For the record, the part number I found online for the discontinued 2002 LX A/T ECM is "37820-PLM-439". Nothing I found matched this (which I believe is a parts counter number, not assembly line.) What I found on the cars is "*** -PLR-A53" and "***-PLR-L55". "***-PLR-A53" is what we brought home. I also grabbed a couple sets of the Blue, Brown, Black relays that sit in front of the ECM, just in case. More on this later!!!
When I got home I decided to do a test to see if the original ECM is actually damaged... I mentioned the "Failed Linking" message on my OBD scanner... and this will be my simple litmus test. I unplugged the battery, removed the old ECM and plugged in the replacement ECM loosely (dangling underneath the dash.) Reconnect the battery and found the OBD STILL said "Failed Linking". CRAP! So I decided to replace the Blue, Brown, and Black relays, one at a time. After I replaced the last one (the black one), I found that the replacement ECM and the OBD scanner were finally speaking!!! No check engine light. No flashing green key light. Hooray!!!
Out of curiousity, I left the three replacement relays in and swapped back to the old ECM... still no joy. That ECM is definitely fried.
That's my status so far. I still need to check the alt for strong mounting and clean contact and get an auto locksmith to do update the keys to the replacement ECM. Baby steps, but progress has been made.
I spent the morning tearing in to look at the condition of the alternator mounts. For the record, my lower alternator bolt was tight! There was considerable corrosion on the lower mounting bracket and linkages which I dressed on a bench grinder with wire wheel to clean, and followed up with some sanding for tougher areas. I then primed the bare metal with weld-through primer, which is conductive. For the upper mount, I sanded to clean up dirt and corrosion, then used a product called Kopr Shield, which has a high copper content which ensures electrical contact and minimizes future corrosion.
I also dress all nuts and bolts that would be making a grounding connection, cleaning them and coating with the Kopr Shield. Threads get a lick of anti-seize, which is a common practice I use to keep threading things happy and moving easily. Finally, I created a bare wire grounding lead, which I attached to the alternator via one if its case bolts and then terminated to the body with a sheet metal screw at radiator support/tie bar. This may seem like a hack solution to some, but it does do the job very well, as you can see from the photos attached that there is continuity between the alternator case and battery (-) cable, which is a really good thing.
Grounding is verified!
For the record, it's currently over 98°F outside with high humidity. I had to build a makeshift sunscreen so that I could do this work this morning without suffering heat exhaustion. My solution may not look like much, but boy did it help!
Next steps
Once I get some shade in my work area (the house blocks afternoon sun) I will mount the new ECM in place but not hook it up. I will leave the old ECM dangling down so that I can back out of the driveway and park on the street. Once that is done, I will hook it up and test again to see that the OBD2 scanner can talk to the ECM. With an all clear there, I will button up the glovebox area and wait for the auto locksmith to do his magic. Sanded clean and coated with Kopr Shield. Condition of mounting contacts before Cleaned and coated. Condition of tensioning and mounting hardware before... Even with a tight lower mounting bolt, the condition of the lower bracket was pretty sad. Cleaning up. Very stubborn. About to resort to bench grinder for the second time. Weld-through primer for rust protection and good electrical contact. Added homemade grounding strap to tie the alternator case to the body. Continuity between the battery neg cable and the alternator case means a good solid ground.
Final update
The replacement ECM is in. OBD scanner can communicate. No check engine light. No codes (but that's the deal with disconnecting power.) Still a green flashing key, but we called an auto locksmith who showed up at our doorstep and did the key programming. The Lil'Car runs again! After the key programming, the tach is running again and the car has found its get up and go!
The Honda service to program the keys runs about $150 while the auto locksmith ran $250... but I'm okay with that. We would have had to tow the car to the nearest dealership, which means either a tow truck towing bill ($$$???) or the hassle of renting a U-Haul truck and trailer to two the car ourselves. Either way, that would be at least $100 (the difference between Honda and auto locksmith), if not more plus a tremendous hassle, taking time off from work, and waiting. Instead, it's a Sunday afternoon and the job is DONE!
Thank you to everyone for your input. If anyone has any questions, I'd be glad to comment further.
Cheers!
Michael J
Last edited by michaelj; Jul 19, 2020 at 06:12 PM.
That bracket is pretty sad looking, so much corrosion. Good work on getting it fixed!
Hey man! That bracket could have been the issue, as the lower alt bolt was tight. I hope my hack-job grounding pigtail from alternator casing to body doesn't offend anyone. It's a great idea as an extra measure of insured grounding.
One thing that I want to reiterate is that it appears that at least one of the three relays near the ECM was also part of the problem. At the very least it was part of the OBD port fail linking issue.
When ever I go to a junkyard, I always pull fuses and relays. Having spares of those on hand is priceless when trying to diagnose a problem. Quick swap outs can narrow the focus by ruling out relays/fuses.
Thank you for your patience and willingness to answer questions. More forums would benefit from such support.
ps... would it be helpful for me to write up a step-by-step for getting the ECM out? I've had a lot practice lately (three junkers and one Lil'Car) and can do a removal in about 15 minutes now. Let me know!
The higher voltage alternator readings (14+ volts at start up) have been nagging at the back of my mind. I’ve been curious as to whether the alt is constantly putting out that voltage or if it was just a matter of the battery sitting for a few days and needing an initial top off charge.
Last night my wife and I did a quick trip from DC to Annapolis, MD (about 50 miles on highway round trip) and I’m happy to report that when we got home, I pulled out the multi-tester and checked the engine idling voltage output at alternator positive terminal and various grounding points, specifically the new body ground lead. Voltages came in at 12.38~.40. Perfectly normal and one mental worry item crossed off the list.
