Subaru Won't Run Right After Battery Drained

Michael Mobile Technician Clinton, Utah Posted   Latest  
Case Study
Driveability
2000 Subaru Legacy L 2.5L (6 EJ252) 5-spd (TY754)
Crank /Brief Start
Wont Keep Running
No Codes

So a shop owner asks me to check out an old Subaru that will start and stall. The shop's customer left the key on and it drained the battery. You can keep the vehicle running by continually feathering the pedal until it finally will run. At this point the vehicle will idle but at 1500 RPM. There are no codes even after running for 10 minutes. My first thought was that the throttle body needed to be relearned. Subaru procedure. Disconnect battery, Reconnect battery, Turn on ignition for 10 seconds. I did this with exactly the same result. Since there were no codes, I went into scan data to see if something stood out. MAF function working. MAP function working. The fuel trim was whacked. 36% Long term and -36% short term. I have seen this on GM products where Oxygenated fuel has been used and the customer never fills the tank. There were no resets that I could see in the tool. I decided to clear codes even though there were none. Maybe that would clear the long term fuel correction? I clear the codes. Now the vehicle starts, idles and accelerates. All is good.

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Interesting
Roy Service Manager
Winnipeg, Manitoba
Roy Default
   

Early 2000s Subarus need an idle relearn done if power is removed or battery dead. If you simply start the vehicle after power is restored, and try drive the vehicle... It will end up screwing up idle. It will then stall when the throttle is released, stall at lights etc. The trick is to clear the learned data, and start the car, but dont touch the throttle for 10 mins. You will hear idle…

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Nathan Mechanic
Littleton, Colorado
Nathan Default
 

We usually clean the throttle body on subarus when they do that to.

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Roy Service Manager
Winnipeg, Manitoba
Roy Default
   

Even with a clean throttle body or a new one, it usually needs the IAC relearn. Often, the idle speed is set too low if you mess with the throttle when it is calibrating. Many owners don't know that and find their Subaru stalls when off throttle, after they replace or drain the battery. We have had techs service the cars, and simply drive them out of the bay for a test drive. That fubars the…

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Nathan Mechanic
Littleton, Colorado
Nathan Default
 

Right. We usually clean the throttle body then do what you outlined.

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Agree
Chad Owner/Technician
Cañon City, Colorado
Chad Default
 

I would confirm the throttle body is clean first. Any time the battery is unhooked or the codes are cleared the throttle body will perform a min max calibration on the next key cycle. Another tech in our shop had the same issue last week. I had him clean the throttle badly and clear codes even though no cases were set. You then cycle the key and leave the key in the run position for at least…

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Gary Owner/Technician
Buena Vista, Colorado
Gary Default
 

Thanks for the case studies, Chris. Real-time experience puts a whole new spin on what we know and what we've learned.... Gary

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

So clearing codes when there are none stored, resets fuel trim? Great tip!

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Rudy Technician
Montebello, California
Rudy Default
   

Geoff- This is true of many(maybe most?) cars.

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Helpful
Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

Wow. 17 years of aftermarket training classes and NOBODY ever mentioned that. And I sit in front! Gracias amigo.

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Funny