Author Topic: rough running, CEL & P1312  (Read 316 times)

weetabixface

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rough running, CEL & P1312
« on: 14 June 2021, 01:36:18 PM »
Hi all

this happened to me yesterday afternoon (2008 Aero Estate), third journey that I was having to make after being out in the morning. Very sluggish and unresponsive, needing to go hard on the accelerator to get moving. Pulled over, engine didn't sound right clearly missing, stopped and only on restarting did CEL come on. Cheapo code reader came up with P1312 which WIS is telling me is "Combustion detection cylinder 1+2, open circuit / short to B+" - clearing the code worked briefly but came back so abandoned my journey and crawled home.

I guess I need to pull the plugs on cylinders 1 and 2 to see what state they are in, not done many miles since they were last changed - only the weekly grocery run and occasional trips to the dump, all less than 5 miles. Reading here and elsewhere that code could indicated that the DIC is on it's way out so will have a close look at that - anything in particular I should look out for, cracks etc.

the other thing that is troubling me is when I was out earlier yesterday morning, on leaving the house was sure that the gauge showed I had ~1/4 of a tank. After a journey of some 5/6 miles it was well into the red and the fuel light was on. Not wanting to risk it and knowing I was going to be using the car again later in the day I filled up from a place I wouldn't usually use, with 95 rather than the usual 99, because that is all they had. Coincidence ? I expect if it were missing due to that if that there would be another/different DTC showing.

cheers

W

sgould

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Re: rough running, CEL & P1312
« Reply #1 on: 14 June 2021, 04:02:04 PM »
When you remove the DI cassette, check for a crack.  There is a "traditional 45" crack that occurs.  i've had two failures with this crack.  When I unscrewed the plastic cover with the crack and the four legs in it, I could see evidence of spark etching in the case of the transformer underneath.  The first DI failure only set off a CEL after a full throttle burst, but got worse.  The second one that failed caused bad starting.
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weetabixface

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Re: rough running, CEL & P1312
« Reply #2 on: 14 June 2021, 07:08:04 PM »
Crack exactly like the one in the photo in the section of the DIC above cylinders 3 & 4. A new one is on the way

TomPaine

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Re: rough running, CEL & P1312
« Reply #3 on: 15 June 2021, 07:52:14 PM »
Take a bow Will - that is some remote diagnostics!

Audax

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Re: rough running, CEL & P1312
« Reply #4 on: 15 June 2021, 09:33:48 PM »
Take a bow Will - that is some remote diagnostics!

P1312 and P1314 is 99.999% the DI cassette (or wrong spark plugs fitted). You could have a bot scan peoples posts when they submit a question with that fault code and give them the answer.  ;D

sgould

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Re: rough running, CEL & P1312
« Reply #5 on: 15 June 2021, 11:27:21 PM »
I understand that it's recommended that you change the plugs when you fit a ne cassette.  If a plug is faulty, it can make the DI cassette "work harder" so it get s hotter and fails earlier.  That's what I was told.  It doesn't seem unreasonable.
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Audax

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Re: rough running, CEL & P1312
« Reply #6 on: 16 June 2021, 08:37:42 AM »
I understand that it's recommended that you change the plugs when you fit a ne cassette.  If a plug is faulty, it can make the DI cassette "work harder" so it get s hotter and fails earlier.  That's what I was told.  It doesn't seem unreasonable.

Used to see some DI failures about 10k after being serviced with the wrong plugs at the local Bosch service centre all those years ago, might have been coincidence though! would always replace the plugs after a DI failure even if they were brand new, the cost in the grand scheme of things is pennies overall.

TomPaine

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Re: rough running, CEL & P1312
« Reply #7 on: 16 June 2021, 03:16:59 PM »
Take a bow Will - that is some remote diagnostics!

P1312 and P1314 is 99.999% the DI cassette (or wrong spark plugs fitted). You could have a bot scan peoples posts when they submit a question with that fault code and give them the answer.  ;D

Sure re the fault codes but that is not the most generous interpretation of the exchange: I was referring specifically to the cracks on the DI that Will sent pictures of and which the OP then found on his DI.

Audax

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Re: rough running, CEL & P1312
« Reply #8 on: 17 June 2021, 08:08:07 AM »
Sure re the fault codes but that is not the most generous interpretation of the exchange: I was referring specifically to the cracks on the DI that Will sent pictures of and which the OP then found on his DI.

Think you might have misinterpreted my response a little. Those fault codes pretty much always appear accompanied with the cracks. It's just one of the very common Saab issues that when those codes appear and are *not* a DI failure with a crack it's very unusual. and unexpected.

weetabixface

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Re: rough running, CEL & P1312
« Reply #9 on: 19 June 2021, 09:43:37 AM »
As ever, encyclopaedic knowledge

Thanks for the further advice on switching out the plugs. I did order a new set with the DIC, but for the life of me can't find my gauge to check the gap before they go in

weetabixface

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Re: rough running, CEL & P1312
« Reply #10 on: 19 June 2021, 10:25:37 AM »
further to this

NGK says not to use anti-seize

WIS says use it

Audax

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Re: rough running, CEL & P1312
« Reply #11 on: 19 June 2021, 12:39:36 PM »
Never used anti-seize over hundreds of cars so it's not necessary, they are pre-gapped so just visually compare them to each other if you can't measure them.