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Matt, Engineer
Category: Subaru
Satisfied Customers: 21374
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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I have a '03 Impreza St. Yesterday the AC stopped working.

Customer Question

Hi, I have a '03 Impreza St. Yesterday the AC stopped working. It drove just fine so I checked it after I got home. The belt broke. I got a new one, and the alternator belt and was gonna replace them tonight after work. On the way to work this morning it was running really rough, bucking, misfiring, no acceleration. Same thing all the way home. Wasn't sure I'd make it home. The CEL came on so I checked the codes... 341, 302, 303, 304. 341 says it's the cam shaft sensor. since the engine ran fine until I pulled the old belt off I wondered if I disconnected that. As near as I can tell it's just below the dipstick, and still connected.
JA: How old is the battery? How many miles are on the car?
Customer: Battery is a couple years old. Not sure on the mileage.
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Yes. All I've done is look at the cam shaft connector, and get the engine ready for the new belts. The AC idler is seized so I still have that to buy.
JA: Anything else you think the mechanic should know?
Customer: Not that I can think of. The car was running perfectly before this.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Subaru Mechanic about your situation and then connect you two.
Submitted: 11 months ago.
Category: Subaru
Expert:  Matt replied 11 months ago.


when you say the belt broke do you mean the main timing belt thats under the plastic cover or the smaller ancillary drive belt ?

if its the former then this needs to be set carefully to avoid valves touching pistons and damaging the engine

and if the main belt is OK then yes its possible that either the cam sensors or the crank sensor that are damaged or the wiring to the sensor has been damaged by the AC belt snapping

so check the wiring 1st and if thats OK then replace the cam sensor on the LHS of the engine bay as thats the bank '1'

Customer: replied 11 months ago.
not the timing belt. The small belt that only turns the AC and idler pulley. I'll check the wiring and sensor tomorrow. Thank you!
Expert:  Matt replied 11 months ago.

no problem

just get back to me on this post

Customer: replied 11 months ago.
Progress report... There doesn't seem to be any damage to the wiring for either the cam position sensor or the crankshaft sensor. I unplugged them both, very clean terminals. Plugged them back in firmly. No change, still really rough, barely starts. Next step is replace the sensor. Auto Zone didn't have it, or the idler pulley I need for the AC so tomorrow, my day off, I'll try to make it to the dealer.
Expert:  Matt replied 11 months ago.


if its they are both the older sensor with 2 wires then you can test it by measuring the resistance across the pins as it shoudl be about 200-300 ohms for both

Customer: replied 11 months ago.
Thanks. Will test before I go. If the sensor tests ok is there anything else I should look for?
Expert:  Matt replied 11 months ago.

yes trace the wire back to the ECU checking for damage as you go

ideally do a continuity check between the ECU pins and the sensor socket for both the crank and cam sensors

Customer: replied 11 months ago.
Will do. Thanks!
Customer: replied 11 months ago.
Next update... I replaced the camshaft sensor. Now it won't start at all. Turns over but no firing. Codes are Cam sensor and crank sensor. It looks like there's a splice in the cam sensor wire in an awkward place to get to. Could be it. I pulled the computer so I could run continuity on the wires, but the pin chart I downloaded is a little different than what's on the unit. Tonight's project is locate the right wires, check them and see if the splice is bad. Thank you for your help. Hopefully can finish this quick and get you paid.
Customer: replied 11 months ago.
Well, I disconnected the computer, put 12v on the wires from the crankshaft sensor and couldn't find a match on any of the harnesses. Tried by color, then started going through each pin hoping to find a match. Without the right pinout chart I don't know which ones they should be, and the several I found online are wrong. Then I cut back the wrap on the cam sensor wire and it's not a splice. It's been taped where the shielding ends and the two wires come out. Short length, no breaks. Beginning to wonder if I'm in over my head.
Expert:  Matt replied 11 months ago.


there are several ECU pinouts here

Customer: replied 11 months ago.
Thank you! He has one pdf that shows the plug layouts of different ECU's. This is the first time I've seen the right layout and jack numbers. Mine is F5-a.
Sadly that's all he has and brief search tonight didn't find the pinouts. Will look again tomorrow during work. Thanks!
Expert:  Matt replied 11 months ago.

OK good luck

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