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How to diagnose a 'ER HC' odometer trouble code?

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'ER HC' code problems - Short Version:


2500 miles after doing my head gaskets and timing belt my car stalled out on me getting on the highway and is throwing the 'ER HC' code on the odometer. Won't start now unless I disconnect the battery for a while.


I've checked the obvious spots for electrical disconnections and bad battery contacts. But other then that I'm stumped at how to attack this without having to wave the white flag and have it towed to the dealer and admit ultimate defeat.


But i do have time on my side and was able to tow it back home on my own at least. So i'm not giving up yet.


Longer version with some history:



Got the car to run yesterday for three minutes after disconnecting the battery and the main engine harness under the intake for 10 minutes. Reconnected everything, started up, then died and flashed the ER HC code. Won't start, won't crank again. Something is definitely wrong if the car is starting and then cutting itself out and essentially locking me out of restarting the car.



My thoughts to check next are....

1. Main ground on the frame. Clean that and reconnect?

2. ECM for loose wires under passenger side carpet? ( i doubt its this)

3. Is there a relay or fuse or something I should check? (since it started, then died i dobut thats it either)


Additional info


1. My power steering pump is failing and I've been driving it like this for over week (new one is in the mail). My power steering fluid was low I noticed yesterday. (it wasn't last week)


2. In 2500 miles since head gasket job: My engine has leaked 3 quarts of oil somewhere near the back of the engine and its dripping off of the subframe and transmission. (the underside of the heads and oil pan look clean)


My coolant looks green and clean so my guess is my head gaskets are still good.


3. The car was clicking the day before it died on me on two miles from my house. Turns out my car only had about a quart and a half of oil in it. I put three quarts in and it has held that. The clicking stopped after filling the oil up.


When it died on highway entrace ramp, my girlfriend said she heard the clicking again. (but the oil level shows its ok)


4. It might of run out of fuel 6 hours before it died on the highway. My girlfriend coasted it into the driveway. (I added one gallon of gas, three quarts of oil) and it started fine.


Very stumped.


When I put the key to the on position before starting I sometimes hear a faint strange "wrrrrring mechanical sound' coming from i think the passenger glovebox area. I am sitting in the drivers seat when i hear this noise.


(note: I have a similar response in the warranty section, but I'm way out of warranty so I was hoping to give this topic some love in the main forum)

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Whatever is going on, I'm sorry to say that if you were actually running the car with only 1.5qts of oil in it that an electrical problem is probably the least of your problems. IIRC, the "Er HC" code usually indicates something electrical--could be as simple as a dying battery (get it tested) on to an ECU / ECM.


Good luck.

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Check that giant electrical plug on the passenger side of the engine bay. Its brown I believe. Make sure it is fully plugged in and secured as it uses a type of lock to keep it secured. You'll know what I mean when you see it. Mine was loose and not completely locked in after I did my clutch install and got the same code.
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Yea I did unplug and replug that massive electrical plug on the passengery side. That with the battery disconnect did allow the car to start... for a few minutes before the ER HC returned and dissabled any more starting.


I get a voltmeter in the mail anyday now. Its too cold in new england for the next few days to poke around for a short though.


Test mod connectors? Not sure what or where those are. Maybe I did. But lets keep in mind the car did run great for about 2500 miles between replacing the HG's and car stalling out on the highway.


The check engine light was on before the HG's and after it from a p0420 ineff catalyst.


That code has been on for a couple years and I'm not replacing any parts for that silly code.


I'm not sure if other codes are showing now. I assume there is something. I need to buy a code reader or get my viag com cable to work.

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It looks like using the SSM (Subaru Select Monitor) would show where the break in the communication circuit is exactly.

go through the steps Mspank lists in this post and see what codes you come up with, it will help in figuring out where the next place you should start looking is



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  • 4 months later...

Old thread. But same problem. Yesterday after a few months of sitting I tried to start the car. I unhooked the big engine harness plug and battery, let the ecm reset, then replugged everything in.


Still car won't start. (won't even crank now) ER HC is showing up in the odemeter. Tempature gauge goes all the way to hot and just sits there while the key is turned to the on position.


I pulled the carpet up and looked at my ECM. The green plug is uplugged like its supposed to be.


Interesting thing was that the ECM has masking tape on it that says 'Pilgrim Subaru" with a a Vin number written in Sharpie on masking tape that does not match my car.


So at least 5 years and 60,000 miles ago I think my ECM was replaced once already. (The car ran fantastic while i've owned it until the timing belt blew)


The subaru select monitor? I'm assuming this is a diagnostic tool that I need to tow the car to the dealer to have used on my car right? Thats about what I'm ready to do.


Would love to fix this car.

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Get a hold of a real scanner that can communicate to all the modules. Pull codes, analyze inputs, go from there.

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  • 2 months later...

Just happened 2 miles away from my house in my wagon. Was driving and motor just shut off and I coasted to a stop, with ER HC code on the odometer.


Tried resetting the ECU, checked fuses, checked connectors inside. Had the car towed home found a bit of rust on the backside of the ECU, and some rust got just to the edge of the circuit board of ECU inside the housing. Also started checking wiring, found that the bunch of cables that goes into the harness plug by the turbo, 1 wire got damaged from rubbing against the wastegate bracket or heatshield of the turbo.


going to try to clean it up a bit and tape the wire and see if the car will start. Hopefully thats the problem.

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Taped up the bad wire, still same thing.


If I buy a used ECU to replace, what is the process to get immobilizer reprogrammed to my original keys? Can I just bring the used ECU w/o the car to dealer to get them to do that? or can they only reprogram once everything is hooked up in the car, meaning I have to tow the car to the dealer?

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  • 1 year later...
Old Post but I am experiencing the same issue. I just bought a used Legacy with 117k. Carfax came out clean, but after driving a little while the CEL came on with the P0420. After reading about this issue on this forum I found that it most likely related to the rear O2 sensor. I let it go for 1.4k miles and then I experienced this problem. The car died on me with all of the symptoms as mentioned in the original post. Figuring no one has found a solution to this problem I took it to my local subaru dealer. They diagnosed a failure in the ECU. I bit the bullet and payed dealer prices to change it out. Dealer got me the car back the other day and it ran like a dream. No CEL issues related to P0420. I went for a drive and set the cruise control...BAM CEL pops on with P0420 issue, but I am able to drive no other problems. The next day I go for a drive then the car begins to idle high in park, and as I drive the car begins to jerk while I simultaneously here clicking coming from the passenger side of the car. I experienced a similar issue prior to the car dying on me. I immediately turned the car around and got it home. None of the messages popped up, but I feel that it is inevitable that the car will return to the failsafe mode which started this post. The dealers next thought was replacing the BIU, but I feel they are just throwing parts at a problem. Anyone have any thoughts that I might be able to try? I have check many of the connections and everything seems okay.
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