P1552 fault code - Idle Air Control Valve

[finestjammy]

Hi All

Accelerating onto the motorway and I get a PSM fault, limited engine power and check engine warnings The car gradually lost power and I managed to crawl into a lay by. I have an OBD dongle plugged in all the time and it indicated the P1552 code. I cleared it and all seemed fine.

Now, very bad driving practice but as I've got an OBD dongle that reads out instant MPG I've been playing around as to what influences economy. Contrary to what I though it seems that coasting in neutral gives better MPG, rather than in gear. Where it's been appropriate I've been knocking it into neutral and letting the car coast. Do you think this might have caused a code to be thrown? I.e. the car is 'thinking I shouldn't be moving at speed and coasting'?

I'll put myself on the naughty step and revert to non experimental driving techniques and keep an eye on it. Just wondered if this is the reason the code mu have been thrown

[LiamH66]

Your explanation sounds very plausible. Coasting in neutral will always use less fuel than cruising in gear, but bear in mind that coasting in neutral you are slowing down, and cruising in gear you are holding a steady speed. "Coast and burn" is the driving strategy used by mileage marathon vehicles to get amazing fuel consumption figures, and it definitely works. (They actually shut the engine down entirely while coasting, and restart for the "burn" period). An engine management system set up for the road is unlikely to expect you to be doing this, and most hold a higher idle speed while the vehicle is moving, expecting it to be put into the next gear down at some point in the near future.

Try driving as the engine management system would expect for a while and see if the code recurs. I'm interested!

Liam

(Which model car by the way?)

[finestjammy]

LiamH66 said:

Your explanation sounds very plausible. Coasting in neutral will always use less fuel than cruising in gear, but bear in mind that coasting in neutral you are slowing down, and cruising in gear you are holding a steady speed. "Coast and burn" is the driving strategy used by mileage marathon vehicles to get amazing fuel consumption figures, and it definitely works. (They actually shut the engine down entirely while coasting, and restart for the "burn" period). An engine management system set up for the road is unlikely to expect you to be doing this, and most hold a higher idle speed while the vehicle is moving, expecting it to be put into the next gear down at some point in the near future.

Try driving as the engine management system would expect for a while and see if the code recurs. I'm interested!

Liam

(Which model car by the way?)

Thanks for the response. It's a Cayman S, 987.2. It was me just being daft and playing around really, I'm a serial messer and can't stop myself I'll drive as the ecu intended from now on and keep an eye on it. An interesting little experiment nonetheless.

[Rockster]

finestjammy said:

Hi All

Accelerating onto the motorway and I get a PSM fault, limited engine power and check engine warnings The car gradually lost power and I managed to crawl into a lay by. I have an OBD dongle plugged in all the time and it indicated the P1552 code. I cleared it and all seemed fine.

Now, very bad driving practice but as I've got an OBD dongle that reads out instant MPG I've been playing around as to what influences economy. Contrary to what I though it seems that coasting in neutral gives better MPG, rather than in gear. Where it's been appropriate I've been knocking it into neutral and letting the car coast. Do you think this might have caused a code to be thrown? I.e. the car is 'thinking I shouldn't be moving at speed and coasting'?

I'll put myself on the naughty step and revert to non experimental driving techniques and keep an eye on it. Just wondered if this is the reason the code mu have been thrown

You can avoid the coasting high miler technique but I suspect it won't help. See below for what I have on the error code.

You can try a E-gas calibration. Costs nothing and is worth a shot. The calibration procedure should be in the owners manual.

For my Porsches: With the key off and no pressure on the gas pedal turn the key to the on position and leave on for at least 60 seconds. Then turn the key off and leave off for at least 10 seconds. The next time the engine is started the calibration is complete.

My info on the error is:

P1552
Diagnostic information ­ DME (DFI) control unit
Control unit function monitoring
Diagnostic conditions
Ignition on > 10 second(s)
then idling > 30 second(s)
then engine speed > 1,000 rpm > 60 seconds with:
Vehicle standstill
Possible fault causes
Power supply or ground supply faulty.
See P1559 DME (DFI) control unit software error
Re­program
INFORMATION
All calculations for functions in the control unit are monitored by a higher­level unit. A fault is entered if monitoring detects implausible calculations.

[finestjammy]

Rockster said:

You can avoid the coasting high miler technique but I suspect it won't help. See below for what I have on the error code.

You can try a E-gas calibration. Costs nothing and is worth a shot. The calibration procedure should be in the owners manual.

For my Porsches: With the key off and no pressure on the gas pedal turn the key to the on position and leave on for at least 60 seconds. Then turn the key off and leave off for at least 10 seconds. The next time the engine is started the calibration is complete.

My info on the error is:

P1552
Diagnostic information ­ DME (DFI) control unit
Control unit function monitoring
Diagnostic conditions
Ignition on > 10 second(s)
then idling > 30 second(s)
then engine speed > 1,000 rpm > 60 seconds with:
Vehicle standstill
Possible fault causes
Power supply or ground supply faulty.
See P1559 DME (DFI) control unit software error
Re­program
INFORMATION
All calculations for functions in the control unit are monitored by a higher­level unit. A fault is entered if monitoring detects implausible calculations.

Thanks for that. I've driven 100 miles since the limo mode happened and so far so good fortunately. I've got a durametric which I think can be used to do an e-gas calibration/reset. I'll take a look tomorrow. Thanks again for the input.

[Steve H]

finestjammy said:

LiamH66 said:

Your explanation sounds very plausible. Coasting in neutral will always use less fuel than cruising in gear, but bear in mind that coasting in neutral you are slowing down, and cruising in gear you are holding a steady speed. "Coast and burn" is the driving strategy used by mileage marathon vehicles to get amazing fuel consumption figures, and it definitely works. (They actually shut the engine down entirely while coasting, and restart for the "burn" period). An engine management system set up for the road is unlikely to expect you to be doing this, and most hold a higher idle speed while the vehicle is moving, expecting it to be put into the next gear down at some point in the near future.

Try driving as the engine management system would expect for a while and see if the code recurs. I'm interested!

Liam

(Which model car by the way?)

Thanks for the response. It's a Cayman S, 987.2. It was me just being daft and playing around really, I'm a serial messer and can't stop myself I'll drive as the ecu intended from now on and keep an eye on it. An interesting little experiment nonetheless.

Depends on what the OP means by coasting, if you are totally off the power then the injectors will be entirely shut off above about 1500rpm so zero usage. Neutral and engine off would still be better as there's no engine braking effect so you can coast further.

[finestjammy]

Steve H said:

Depends on what the OP means by coasting, if you are totally off the power then the injectors will be entirely shut off above about 1500rpm so zero usage. Neutral and engine off would still be better as there's no engine braking effect so you can coast further.

I was coasting in neutral, engine on, clutch up. I'd always assumed that when you were off the throttle and in gear would use less fuel than in neutral, as the injectors cut off as you say. According to the instant readout coasting in neutral produces better mpg than in gear.

I've reset the throttle body using Durametric but not had chance to go for a drive yet. Losing power on a busy M1 with no hard shoulder shall teach me to fiddle around . I wasn't actually coasting at that point, I was using a reasonable amount of throttle. I assume it threw a wobbly do to previous coasting of the last 350 ish miles.

Edited by finestjammy on Sunday 25th September 17:33

[Steve H]

finestjammy said:

I was coasting in neutral, engine on, clutch up. I'd always assumed that when you were off the throttle and in gear would use less fuel than in neutral, as the injectors cut off as you say. According to the instant readout coasting in neutral produces better mpg than in gear.

You're original assumption was correct, I'm pretty sure the readings are a quirk of the way the gadget calculates the mpg rather than a real result.

[Pope]

Steve H said:

You're original assumption was correct, I'm pretty sure the readings are a quirk of the way the gadget calculates the mpg rather than a real result.

Quirk is right;
30mpg driving with cumulative in gear overrun for two miles = 30mpg

30mpg driving with cumulative neutral idling for 2 miles @ 60-70mph = 40mpg

Porsche don't do instant fuel consumption readout but most other VAG group cars do; knock into neutral and idle coasting at 70mph returns 200mpg.....

[finestjammy]

Morning all, bit of an update. All was fine for last 300 miles ish, I did a throttle body reset via Durametric. Popping to the dentist this morning, cold engine and pulled out a junction and the same sequence happened again. PSM failure then check engine light. Pulled up, cleared the code and all was fine again. As this car doesn't have an 'idle control valve' would it be a throttle body fault? I'd washed the car the evening before, any linkage to the fault donyou think?

Any help appreciated.

James.

[la3541]

I have a 2012 Boxster S and as I was pulling away from a stoplight this morning I got the p1552 code. It is the first time it has happened to me. I also was able to clear the code with the obd gadget and everything seems ok now. I drove the car for another 10 miles or so and the code did not recur. I also had the car washed yesterday. Please let me know if you find out what caused it.

[finestjammy]

Bit of an update. Took it to the OPC and they reset everything via PIWIS. Seemed to do the job...until today whilst on holiday. Accelerating up hill, medium throttle and the PSM/ABS plus reduced engine power warnings came on. Turned the engine off and restarted, the check engine/visit workshop light remained solid. From what I've searched I think it might be the MAF starting to fail. It's always under load when it happens and makes no difference if it's in a corner or in a straight line. Booked in a week tomorrow for a diagnosis.

[gadgit]

This fault can also be triggered by the brake switch.
This has been a problem on the 981 on early production models.

Turned out on the 981 that is was just a spacer that would not allow the full return of the brake pedal and electrical contact was not clean in the brake system, which logged a PSM fault.
Also, I had a Mercedes B class that did it to me. Went to limp mode.
I just changed the brake switch £12..... And it disappeared.

This is a common problem on some german cars.
This might not be your problem, but so many others things cause this problem as well.

Gadgit.

[finestjammy]

gadgit said:

This fault can also be triggered by the brake switch.
This has been a problem on the 981 on early production models.

Turned out on the 981 that is was just a spacer that would not allow the full return of the brake pedal and electrical contact was not clean in the brake system, which logged a PSM fault.
Also, I had a Mercedes B class that did it to me. Went to limp mode.
I just changed the brake switch £12..... And it disappeared.

This is a common problem on some german cars.
This might not be your problem, but so many others things cause this problem as well.

Gadgit.

Thanks for that. The CEL light has now extinguished itself, I know it will return if I don't drive like there's an egg shell under the throttle pedal though. I haven't noticed a pattern of it happening after braking, always under power, still worth a mention to the OPC though. Thanks again.

[Steve H]

My Cayman had a brake light switch but it didn't flag any codes, symptom was intermittent zero throttle response for a second or two as I went on the gas.

[finestjammy]

A little update to this thread. Not confirmed as yet, but the root cause of my problems might be the dongle being plugged in in the first place, how embarrassing

The service manager is taking it home tonight for a good testing.

A quick google and it seems OBD readers/dongles aren't merely a slave device receiving data. Others, admittedly, not Porsche, have had similar issues to me.

The push for third parties to get us using dongles for various purposes seems a little worrying. TOM TOM are even getting in on the act, I haven't seen any warnings on the use of them though. Buyer beware I guess.

I await the final conclusion before I take the walk of shame back into the service department