Skoda Fabia 1.4 17961 - Barometric / Manifold Pressure Signals

[jverdicchio]

The VAGCOM faults I've recorded on my skoda Fabia have been persistent but not critical until recently . It started off 55631 miles as:

Address 01: Engine        Labels: 036-906-034-APE.lbl
   Part No: 036 906 034 DF
   Component:  MARELLI 4MV G      5954  
   Coding: 00071
   Shop #: WSC 13765  
   VCID: 59B951E2C3456F8EAD-4B1A
   TMBMD46Y274094010     SKZ7Z0F3857289

2 Faults Found:
17961 - Barometric / Manifold Pressure Signals 
            P1553 - 35-10 - Implausible Correlation - Intermittent
17912 - Intake Air System 
            P1504 - 35-10 - Leak Detected - Intermittent
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 6R0-907-37x-ASR80.lbl
   Part No SW: 6Q0 907 379 AG    HW: 6Q0 907 379 AG
   Component: MABS 8.0 front  H05 0002  
   Revision: 00000000    Serial number: 00000000000000
   Coding: 0002178
   Shop #: WSC 13765 790 00000
   VCID: 020B568E5E530C569C-5124

2 Faults Found:
01314 - Engine Control Module 
            013 - Check DTC Memory - Intermittent
             Freeze Frame:
                    Fault Status: 00101101
                    Fault Priority: 2
                    Fault Frequency: 5
                    Reset counter: 102
                    Mileage: 88652 km
                    Time Indication: 0

18265 - Load Signal 
            P1857 - 000 - Error Message from ECU - Intermittent
             Freeze Frame:
                    Fault Status: 00100000
                    Fault Priority: 2
                    Fault Frequency: 5
                    Reset counter: 102
                    Mileage: 88652 km
                    Time Indication: 0

___________________________________________________

The car seemed OK and drove OK. I've checked the air intake manifold is secured down. The air hoses look OK from a rough visual inspection. Recently it has started playing up and going into a "limp-home" mode. The engine warning light would come on. The wife has had to stop the car and engine for a few minutes, the warning light would go away then it seems to be OK and she could carry on. Today it appears to be a permanent state. The VAGCOM gives this:

Address 01: Engine        Labels: 036-906-034-APE.lbl
   Part No: 036 906 034 DF
   Component:  MARELLI 4MV G      5954  
   Coding: 00071
   Shop #: WSC 13765  
   VCID: 59B951E2C3456F87BE-4B1A
   TMBMD46Y274094010     SKZ7Z0F3857289

4 Faults Found:
17586 - Linear O2 Sensor; Pump Current 
            P1178 - 35-10 - Open Circuit - Intermittent
17550 - Load Calculation Cross Check 
            P1142 - 35-10 - Lower Limit Exceeded - Intermittent
17961 - Barometric / Manifold Pressure Signals 
            P1553 - 35-10 - Implausible Correlation - Intermittent
17912 - Intake Air System 
            P1504 - 35-00 - Leak Detected
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 6R0-907-37x-ASR80.clb
   Part No SW: 6Q0 907 379 AG    HW: 6Q0 907 379 AG
   Component: MABS 8.0 front  H05 0002  
   Revision: 00000000    Serial number: 00000000000000
   Coding: 0002178
   Shop #: WSC 13765 790 00000
   VCID: 020B568E5E530C5F8F-5142

2 Faults Found:
01314 - Engine Control Module 
            013 - Check DTC Memory - Intermittent
18265 - Load Signal 
            P1857 - 000 - Error Message from ECU - Intermittent

-------------------------------------------------------------------------------
Address 09: Cent. Elect.        Labels:. 6Qx-937-049-C.lbl
   Part No: 6Q1 937 049 D
   Component: 0000 BN-SG.         1S34  
   Coding: 25774
   Shop #: WSC 13765  
   VCID: 3C77E8762C37BAAF85-5124

1 Fault Found:
01598 - Drive Battery Voltage 
            07-10 - Signal too Low - Intermittent

_____________________________________________________

Looking through the forums the MAP sensor seems a likely culprit for the P1553 and P1504 errors. The P1178 error is possibly a lambda sensor. I've given the MAP sensor a clean with electronic contact cleaner. Still have the same issues. I have a new MAP but at £50 I'd like to be sure this is the main culprit before fitting it. The parts dealer will refund my money if the part stays in its packaging.

 

I've also seem forum posts where these faults leading to: bad coil that become timing belts; EGR valves -  I this engine has one, then I'm not sure where it is.

 

The engine  doesn't seem to rev above 1500rpm ( I think this is what the wife is calling "limp-home mode") . It also idles erratically. I thought I'd include a picture of the engine as sometimes it can be tricky for people to know exactly what sort of car you have from the description (well, I find it tricky). 

 

If anyone can shed some light on this I'd be very happy.

[Breezy_Pete]

The EGR valve is ringed in green in this copy of your photo. Wouldn't expect it to be relevant to your current faults, it tends to get its own fault codes.

 

The pipe I've added a few red lines on is the brake servo vacuum hose. these have a nasty habit of splitting at the terminations of the hard plastic sections, and causing air leaks.  Often these splits are on the underside, out of sight. Feeling with fingertips or photo capturing with phone camera are alternative ways of checking for this.  Either side of the non-return valve just to the right of my last red line is a 'popular' fail site.

 

[sepulchrave]

All of your engine codes and the rough idle and limp mode could be caused by just one split in the brake servo vacuum pipe so a rough visual inspection will not suffice.

You should also check that the alternator is working properly by checking the output voltage, it must be 14.4V +/- 0.1V, no other value will do.

[jverdicchio]

Wino and sepulchrave. Thank you very much for your prompt response and stunningly accurate information. I've found the break servo line split exactly where wino said the common failure point was. I've wrapped some duct-tape around the split pipes to check this was the only issue and the error codes have vanished. I'm off to the parts dealer on Monday to return the MAP sensor and purchase a new brake servo hose.

 

I checked the battery voltage with the engine running and I'm getting 14.4V . 

[Breezy_Pete]

[jverdicchio]

A new piece of vacuum house helped for a few minutes. However, the engine is doing its eratic idle, you can't rev the engine. 

VAGCOM gives:

-------------------------------------------------------------------------------
Address 01: Engine        Labels: 036-906-034-APE.lbl
   Part No: 036 906 034 DF
   Component:  MARELLI 4MV G      5954  
   Coding: 00071
   Shop #: WSC 13765  
   VCID: 59B951E2C3456F87BE-4B34
   TMBMD46Y274094010     SKZ7Z0F3857289

2 Faults Found:
17961 - Barometric / Manifold Pressure Signals 
            P1553 - 35-00 - Implausible Correlation
17912 - Intake Air System 
            P1504 - 35-10 - Leak Detected - Intermittent
Readiness: 1010 0101

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 6R0-907-37x-ASR80.clb
   Part No SW: 6Q0 907 379 AG    HW: 6Q0 907 379 AG
   Component: MABS 8.0 front  H05 0002  
   Revision: 00000000    Serial number: 00000000000000
   Coding: 0002178
   Shop #: WSC 13765 790 00000
   VCID: 020B568E5E530C5F8F-5142

2 Faults Found:
01314 - Engine Control Module 
            013 - Check DTC Memory - Intermittent
18265 - Load Signal 
            P1857 - 000 - Error Message from ECU - Intermittent

-------------------------------------------------------------------------------
Address 09: Cent. Elect.        Labels:. 6Qx-937-049-C.lbl
   Part No: 6Q1 937 049 D
   Component: 0000 BN-SG.         1S34  
   Coding: 25774
   Shop #: WSC 13765  
   VCID: 3C77E8762C37BAAF85-5124

1 Fault Found:
01598 - Drive Battery Voltage 
            07-00 - Signal too Low

 

I've felt over any "air related" pipe going to//from the inlet manifold. They all seem OK, no splits. taken the easy-to-take ones off and blown into them , no obvious leaks either.

 

I assume that if the engine reports "Implausible Correlation" then there must be 2 pressure sensors and one of them does not agree with the other. I've used the graph capability within VAGCOM to plot the two pressure outputs I could find. Does anyone know which of the two "intake manifold pressure" readings relate to which sensor?

The other end of the scale is 1000mbar.

[sepulchrave]

There is only one MAP sensor, you may have a manifold leak since there is no other plausible source for it now that you've fixed the vacuum hose.

[Breezy_Pete]

8 hours ago, jverdicchio said:

I've felt over any "air related" pipe going to//from the inlet manifold. They all seem OK, no splits. taken the easy-to-take ones off and blown into them , no obvious leaks either.

 

Some possible non-obvious leaks might include the EGR valve not shutting properly/completely; the EVAP purge valve doing the same; the PCV valve diaphragm having ruptured.

 

The latter may be easy to detect by putting a finger over the pressure equalisation port on the side of the diaphragm case (hoping to not feel strong suction, at idle), I may have a photo of this port, I'll edit it in if I can find it.

 

 

EVAP valve can probably be investigated by clamping its outlet hose flat near the connection to the manifold, and seeing if the fault goes away.

Edited 21 July, 2019 by Wino

[jverdicchio]

I've checked the voltage at the MAP sensor. 5V for the two inner pins and 0V for the two outer pins.

I removed the MAP sensor and attached some hose over the sensor. I plugged in the VAGCOM and measured the Intake manifold pressure (the two in the above picture). By sucking on the tube I created a partial vacuum. VAGCOM reported that the pressure dropped and both values almost simultaneously. I think this means the MAP is OK. Suggesting that there is a leak somewhere.

 

When I was checking the engine initially, I took off the rocker cover oil filler. I mis-assembled it and in getting the oil filler off I've bent the pins that hold it firmly in place. Does the cavity under the rocker cover form part of the intake manifold pressure? I ask as the oil filler is no longer firmly attached and air can definitely get in.

Edited 21 July, 2019 by jverdicchio

[sepulchrave]

Yes of course the oil filler cap needs to be airtight. Congrats you've found the air leak.

[jverdicchio]

I can not thank you chaps enough for all the help. 

[Breezy_Pete]

28 minutes ago, jverdicchio said:

Does the cavity under the rocker cover form part of the intake manifold pressure?

 

It's connected via the PCV valve, to a greater or lesser extent depending on the valve's openness/closedness.

Fixing this filler cap leak will fix your troubles, almost certainly.