I have a 2008 Skoda Fabia 1.2 petrol with Just 62K miles on it and i have the fault code P1156 on it , If i try to delete the error codes, it will not clear, it stays even after running, a code read / code clear with a scan tool

 

 

Heres a rundown of the issues:

 

Car has intermittent rough idle, missing etc, sometimes you start it up and it seems to run fine, turn it off and on, them its running a bit rough, lumpy idle and abit hesatiant

 

the code always present is , (from my maxidiag scan tool)

 

17564 - Manifold pressure sensor (G71): Open Short to ground : P1156

 

 

once you start and run the car, like i did this morning it run fine on first start up, reved up and seemed to run just  fine, turn it off and started agian, it then run abitting lumpy, rough idle ,  a bit hesiatant etc

this caused it to turn on the engine warning light 

 

now when i read the codes again we get another code appear

 

17564 - Manifold pressure sensor (G71): Open Short to ground : P1156

and

17549 Load calculation cross check: Implausible value: P1141 static  - output dose not sw./short to earth

 

engine light is now on

 

 

what i have done: 

 

1) replaced the map sensor with a brand new one (bocsh) - did not fix the problem

2) looked all over the wiring for a clear break or similar problem, nothing present it seems

 

help me please with a suggestion of a route to take:

 

1) if it says short to ground on P1156 fault code and that is always present even after clearing the codes, does this suggest a wiring fault/break ??

2) if it is a wiring fault what it the bast way to test to confirm a broken wire

3) is there a common place the wires tend to break on these

 

 

has anyone ever had one of the wires break and if so where was it?

 

does anyone have a wiring diagram for the wires running from the map sensor and where they go to ??

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Please supply engine code (BBM or BZG?) or VIN.

There are two different 2008 1.2 petrol mk2 engines, one with 6 valves the other with 12. Finding the right wiring info probably depends on which you have.

 

its a BZG

 

skoda fabia 1 htp70

Wires from the sensor plug are as follows:

Pin 1 Brown wire, earth, test for 0 Ohms to battery negative.

Pin 2 Green wire, Intake Air Temperature sender to engine ECU pin 56 (on the smaller of the two connectors)

Pin 3 Red/green wire, +5V supply from engine ECU pin 62

Pin 4 Brown/white wire, pressure sensor output to engine ECU pin 70

 

Continuity test those if you can, then test for shorts between pin 1 and each of the others.

 

i will give it a test tomorrow if its not raining and post a update on this , thanks

 

on this care where is the ecu located ?? is it the box behind the battery or in a diff location

Flat metal box, on the firewall behind airbox.

just tested

 

Pin 1 Brown wire, earth, test for 0 Ohms to battery negative.

 

i get 02.3 testing this wire

 

i get the same 02.3 testing the the battery negative cable 1 inch apart

 

would this suggest the  brown earth wire is ok

is there a picture of the ecu pinouts on here by any chance??

8 minutes ago, xop321 said:

is there a picture of the ecu pinouts on here by any chance??

there is now:

 

 

so on

 

Pin 2 Green wire, Intake Air Temperature sender to engine ECU pin 56 (on the smaller of the two connectors)

 

 -- i should test at map sensor connecter - to ecu connecter pin 56, and see a ohms reading - if theres no reading this would suggest a wiring break/fault??

 

Pin 3 Red/green wire, +5V supply from engine ECU pin 62

 

 -- i should test at map sensor connecter - to battery  negative to see a  5v reading ( is this only with ignition on / or does it need engine running) - if theres no reading this would suggest a wiring break/fault??

 

 

Pin 4 Brown/white wire, pressure sensor output to engine ECU pin 70

 

--  -- i should test at map sensor connecter - to ecu connecter pin 70, and see a ohms reading - if theres no reading this would suggest a wiring break/fault??

Yes to all of that I think, including the bit about ignition on, you wouldn't get the engine running with that connector unplugged from ECU.

You may find that you need a fine piece of wire to poke into the ECU loom connector to be able to contact your meter probe.

I think the pins in the ECU male part are very thin so you won't be able to get contact in the female loom connector without such a 'probe'. (unless you go can go in from the wire entry side?) Can't remember if that's possible/easy.

 

Edited 8 December, 20232 yr by Breezy_Pete
spelling nd stuff

Don't forget to check for short (0 Ohm) problems between each sensor connector pin and earth.

i just tested all the connecters

 

 

Pin 1 Brown wire, earth, test for 0 Ohms to battery negative.

result = i get 02.3 testing this wire

 

Pin 2 Green wire, Intake Air Temperature sender to engine ECU pin 56 (on the smaller of the two connectors)

result = 01.5 ohms testing this wire

 

Pin 3 Red/green wire, +5V supply from engine ECU pin 62

result = 4.9v with ign on

 

Pin 4 Brown/white wire, pressure sensor output to engine ECU pin 70

result = 0.15 ohms

 

 

this must be a intermitant issue, as now clear the codes - i start the car from cold after doing all the tests and it runs fine, running normal, no codes being fired off, code reader comming back no codes at all

 

the wierd thing is that the code i could not clear yesterday - 17564 - Manifold pressure sensor (G71): Open Short to ground : P1156  - is now cleared

 

just run it for a few mins and it has yet to  show any codes again

 

 

would this suggest i might have a problem either with the wiring still, say once you start driving and moving the wire break might just move enough to break the connection, just when i tested its all in alignment ??

 

could there be a issue in the ecu causing this

 

its just strange its all clear running fine one mintute , then maybe the next day we get the faults back

 

i did not test

 

----- Don't forget to check for short (0 Ohm) problems between each sensor connector pin and earth.

 

so with that just check pins between earth and each pin??

 

like pin 1 to earth, pin 2 to earth, pin 3 to earth, pin 4 to earth, should i see a reading or no readings?? 

Edited 8 December, 20232 yr by xop321

Pin 1 is earth, so just measure from it to each other contact, 2, 3 and 4.

Should be no connection.

It does look like it may be an intermittent problem, possibly a bad/dirty connection? 

Any sign of fluid having got into either sensor or ECU connector housings?

its now fitted with a brand new bosh sensor so i think we can rule the sensor its self as the issue out

 

when i pulled the 2 connecters off the ecu all the connecter pins seemed fine and free of corrosion

 

i did not open up the ecu to just check if any water has gotten into it

 

i will test the pins again like you mentioned and pull the ecu off and open it up  to see if any water has gotten into it and let you no how i get on

 

also would a complete wire bypass be a option, i no its not the best solution, but maybe run new wires from the ecu around and down to the sensor and splice them in, in effect bypassing and suspect broken wires

should i just join the wires on the exsiting wires near the ecu and down near the sensor, i no this is a bodge and not ideal but whould be easier than trying to trace a interminant wire break issue?? 

 

what grade are the correct wires to buy on ebay to do this, do i need smaller gauge wire??

Edited 8 December, 20232 yr by xop321

Do not open the ECU, that's not what I meant. I meant has any pin contact got visible corrosion or wetness, which you have answered.

 

Just on my way to a christmas party, can't help more today.

 

just a quick question about

 

Pin 3 Red/green wire, +5V supply from engine ECU pin 62

result = 4.9v with ign on

 

does the ecu supply the 5v feed from the ecu end down to the map sensor??

 

i am thinkining about adding in the bypass wires, just wondering wehter the 5v feed is threw the ecu or it comes from a different place

 

 

 

Pin 1 Brown wire, earth, can just be earthed to the negaitive battery point with a bypass wire

 

Pin 2 Green wire, Intake Air Temperature sender to engine ECU pin 56 - just run a bypass wire from the ecu area down to just near the map sensor

 

Pin 3 Red/green wire, +5V supply from engine ECU pin 62 - - just run a bypass wire from the ecu area down to just near the map sensor ( is this ok, is the 5v feed comming off the ecu)

 

Pin 4 Brown/white wire, pressure sensor output to engine ECU pin 70 - - just run a bypass wire from the ecu area down to just near the map sensor

 

 

Yes, the 5V rail is generated within the ECU, but I believe it also goes to other items via splices/joins within the engine loom, so I would not advise bypassing that one unless you leave the existing wire in place, and just parallel onto it.

Thinking about it, if that 5V supply had a wiring problem it would probably give intermittent faults on other sensors that it supplies (depending on where the fault is in relation to the splices), so I would probably conclude that one is fine.

 

 

Edited 9 December, 20232 yr by Breezy_Pete

i was thinking of running parallel lines to all of them

 

i will try and post a update latter to see if this sloves the problem

just to let you no, the wiring bypass has now sloved the problem, i have done nearly 100 miles in the car with no problem

 

when i was doing the bypass i noticed the main wiring loom that runs from the body onto the engine was resting on top of the gear linkage

 

so every time the gear lever was being moves we could have had this rub up against the wiring loom, the must by some sort of interminant break between the ecu and the sensor

 

i no a wiring bypass is not ideal , but its sloved the problem

 

thanks breezy pete for the information, i could not has sloved the issue or fixed it this fast without your help

Edited 15 December, 20232 yr by xop321