M and s lights

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
S

sniper3

Member
Posts
20
Discovery 2 v8

No m and s light on startup! All gears select perfectly, xyz switch has been replaced.

When driving the car gets to around 3000rpm (still in first gear) immediately the m and s lights come on and the car goes into limp home mode.

This is a consistent fault any ideas?

There was a MAF fault this has recently been replaced and now there are 2 oxygen sensor errors. Could this be the cause?

Thanks
 
M &S have nothing to do with engine management sensors, except the throttle position sensor...it seems yours enters in limp mode generated by the gearbox management and there could be 14 reasons for that...get it plugged in diagnostics that's the most direct way to find the fault
 
I have had the fault codes read by a local specialist. I think it came back with a communication error or something along those lines. The guy said replace the MAF first and go from there...as he seemed to think it could be a driver demand fault. Other than that he thought it could be a wiring loom fault...but I cant find any obvious signs of chafing or wear. Could it be the gearbox ecu?

Thanks
 
find other 'specialist' if this one told you to replace the MAF to get rid of the M & S lights:violent:

"driver demand" fault comes out of engine ECU when the throttle position sensor is faulty,

and yes there are fault codes with CAN (controller area network) - comunication failures which could cause the limp mode and if this was the fault the looms and connectors must be investigated... also the ECU may missbehave some times ...the exact fault code would have helped me to help you more
 
Well I guess ill find another specialist then haha!!

They used autologic which didnt give specific codes only messages. And im sure it was something along those lines. I guess that would be the next step anyway.

Do you know if the gearbox loom is the same as the td5 as theres a couple on ebay but no v8 ones

Thanks
 
i meant de fault code description not necessarily the number, autologic is a good tool so it must have been accurate, if it was something with "CAN..... " then it's possible to be a datalink interruption, if you can handle a multimeter and you have RAVE as to see the connector views i can tell you how to check the continuity of the datalink... the tester would not give fault codes especially for the gearbox loom just O/C or S/C for the gearbox valve block solenoids or the XYZ switch, the comunication link fault codes are for the CAN datalink which is between the transmission ECU and the engine ECU

check for oil in the engine ECU red plug as the CAN pins are there and a massive oil ingress might disturb it, not common but worth a check
 
I have a rave manual and am aware of how to check continuity so I guess that will be my next job.

If i am correct its the yellow wire and the white wire. Ill check it out when we get some half decent weather and let you know how I get on.

Thanks for the advice
 
you can find the connector views and pin disposals in RAVE -Electrical library, check continuity from engine ECU red plug C0158 pins 32 and 35 to transmission ECU same colour wires...white and yellow as you well supposed...good luck... it woyuld be good to know the exact description of that fault code though to restrict the research area

in RAVE see workshop manual - automatic gearbox - operation...there's a table with the fault codes, maybe you recognise which one of them it was
 
sniper3 said:
I have a rave manual and am aware of how to check continuity so I guess that will be my next job.

If i am correct its the yellow wire and the white wire. Ill check it out when we get some half decent weather and let you know how I get on.

Thanks for the advice
Click to expand...
Forget checking the Can bus wires,there wont be anything wrong with them.This is the first mistake most people make when they see Can faults.Its only two wires twisted together between the engine and gearbox ecu's on a DII.(More complex on later cars,more ecu's are included)
What will be wrong is that the engine ecu will have failed to send a message out onto the can for the autobox ecu to receive.After failing to send about 6 times,(From memory)the autobox ecu will have failed to receive the message.So it just assumes the Can has failed,goes into limp mode,logs Can faults and goes into limp home mode.This is a more interesting process on a RRS or D3/4 where you can follow the faults all around the car.
There can be plenty of reasons for the engine ecu to fail putting out the required message,often a poor running engine failing to make sufficient power for an upshift.A low reading Maf is prime candidate for this as it will severely limit injector pulse widths for a given airflow.This means the engine runs lean and the oxygen sensors cant switch up rich to get them cycling.The engine ecu will them log fuel trim and Oxygen sensor faults.
Can faults do occur, but you would also find similar faults in the engine ecu,and not be able to carefully drive around the fault to keep it from showing up immediately.
 
:frusty: just realised it's about V8 not Td5(that's why i said about oil in ECU red plug :(... and if eightinavee sais the MAF can affect the M & S i can't argue cos i dunno much about V8 management... on a Td5 the MAF can't do that, and that's certain...unless it's short circuit on it then maybe...sorry for my lack of attention about the engine:eek:
 
Last edited:
The MAF has been replaced with a brand new one and no longer shows as a fault in the ecu. After replacing now I am getting o2 sensor circuit malfunction (bank 1, sensor 1)Front sensor LH bank stoichiometric ratio outside operating band and o2 sensor circuit malfunction (bank 2, sensor 1)Front sensor RH bank stoichiometric ratio outside operating band.

I fail too see how this can cause a gearbox fault though. The engine runs fine.
 
I did have them read yes. There was only one fault came back and the guy said it was a communication error and pointed me in the direction of first replacing the MAF and then said trace a possible wiring fault
 
And not after i replaced the MAF no. if that's what you meant....don't fancy paying another £30 to see the same fault lol
 
sniper3 said:
The MAF has been replaced with a brand new one and no longer shows as a fault in the ecu. After replacing now I am getting o2 sensor circuit malfunction (bank 1, sensor 1)Front sensor LH bank stoichiometric ratio outside operating band and o2 sensor circuit malfunction (bank 2, sensor 1)Front sensor RH bank stoichiometric ratio outside operating band.

I fail too see how this can cause a gearbox fault though. The engine runs fine.
Click to expand...

You may think the engine is running fine - it clearly isn't. What needs to be done is an adaptive reset now you have a new Maf fitted.What is wrong is that the long term fuel trims will be so far out even though the Maf is now reading,you wont yet get the short term trims close enough to allow continual closed loop operation.
There is no gearbox fault,its just the gearbox ecu complaining because its not getting plausible info from the engine ecu.Get the engine running well and it will then send the right data to the gearbox for it to make decisions about gear shifts etc.
The Bosch equipment fitted to the Thor engines in P38's and DII's is VERY fussy regarding Maf readings and fuel trims,and will wimp out to open loop very quickly.Luckily a dying Maf is usually the culprit,so easy to sort....
 
sniper3 said:
And not after i replaced the MAF no. if that's what you meant....don't fancy paying another £30 to see the same fault lol
Click to expand...
too bad:mad:;)

in this case if it was read from the EAT ECU it must have been

P1841(16) -* CAN bus fault = Maintains current gear in low range, limp home mode in high range. Shift pressure to maximum, harsh gear shifts/engagement.

.. in this case all the documents are pointing to wiring issue or ECU internal failure... but as i said i'm not the man to speak about V8 management unfortunately:eek:

would have been good to know for sure the exact code description though, and won't hurt to check the continuity of the datalink IMO just to rule it out as even a twisted pair of wires could be interrupted some times ;)
i'm not speaking from experience now just using logic and the documentation cos it's possible to be a fault triggered by the engine ECU too:

P0600 - Serial communication link malfunction = CAN time out

so if we knew exactly the code we could reduce the area as in RAVE at engine management they say:
Controller Area Network (CAN) system
The controller area network (CAN) system is a high speed serial interface between the ECM and the Electronic
Automatic Transmission (EAT) ECU. The CAN system uses a 'data bus' to transmit information messages between
the ECM and the EAT ECU. Because there are only two components in this CAN system, one will transmit information
messages and the other will receive information messages, and vice-versa.

Conditions
The CAN system is used by the EAT ECU and the ECM for transmission of the following information:
l Gearshift torque control information.
l EAT OBD information.
l MIL request.
l Vehicle speed signal.
l Engine temperature.
l Engine torque and speed.
l Gear selected.
l Gear change information.
l Altitude adaptation factor
l Air intake temperature
l Throttle angle / pedal position

Function
The CAN system uses a twisted pair of wires to form the 'data bus' to minimise electrical interference. This method of
serial interface is very reliable and very fast. The information messages are structured so that each of the receivers
(ECM or EAT ECU) is able to interpret and react to the messages sent.
The CAN 'data bus' is directly connected between pin 36 of connector C0637 of the ECM and pin 16 of connector
C0193 at the EAT ECU, and pin 37 of connector C0637 of the ECM and pin 44 of connector C0193 at the EAT ECU.
The CAN system can fail in the following ways:
l CAN data bus wiring open circuit.
l CAN data bus wiring short circuit.

In the event of a CAN data bus failure any of the following symptoms may be observed:
l MIL illuminated after 2 drive cycles (NAS only).
l EAT defaults to 3rd gear only.
l Harsh gearshifts.
l 'Sport' and 'manual' lights flash alternately.
Click to expand...

though, based on the "conditions" i can't see how the MAF would affect the CAN message interchange:confused:
 
Last edited:
Thanks for the info mate. I guess I'll go back and get the values reset. Can they do this with autologic??
 
The guys auto logic didnt display the error codes as in RAVE which is a bit annoying because its not helped me pinpoint the fault at all....only a message and that wasn't in plain English it was full of dashes and all sorts of gobbldy gook. But the guy said it was a comm. fault soo :/
 
You must log in or register to reply here.

Similar threads

Heathereviemay
M and S flashing
Replies
3
Views
629
MJI
MJI
bukko
Disco 2 More XYZ issues
Replies
14
Views
1K
sierrafery
sierrafery
D
P0705 Code
2
Replies
36
Views
2K
Stanleysteamer
Stanleysteamer
S
D2 td5 new electric gremlings (brakes, gearbox, M+S)
Replies
14
Views
1K
suprlite
S
H
Chasing down engine vibration/judder
Replies
6
Views
544
Nodge68
Nodge68
Back
Top