Thread: Causes and Solutions - Flashing M&S Lights

Whilst there is a good recent thread on this problem, I thought it was worthwhile pulling together all of the causes and solutions to flashing M&S lights.

The following have been discussed on the AULRO website from time to time as causes of the M&S lights illuminating. Typically associated with this are the gear selector LEDs and display flashing; as well as the automatic transmission being put into ‘limp home’ mode, with only 3rd and 4th gears being selected by the ECU, to protect the transmission.

Low Battery
A low battery may cause the M&S lights to illuminate. From reading AULRO and tests others have done, this appears to occur around 11.6 volts or lower. If the battery is on the way out, then the voltage drop when starting the vehicle will be sufficient to get the M&S lights going.

Remedies
Charge the battery, check its condition and age, check the charging circuit as to why the battery is low, see if there is a high residual battery drain when the ignition is off, change the battery to an equivalent of at least OEM specification.


Gear Position Switch / XYZ Switch
BTW: This is the typically the first solution everyone suggests.
The gear position switch (inhibitor switch, xyz switch) is a leading cause, but not the only one and without diagnosis or inspection, prior to replacement, may or may not fix the fault. This is a $300 (replacement cost) choice or a couple of hours taking it off, pulling apart etc on a maybe??

A quick test, suggested by Disco Muppet, may help you to determine if you should look at the switch

"Apparently a quick and simple test for the xyz switch is to put the windscreen wipers on
If you put your wipers on, then select reverse then the rear wiper should come on, of the xyz switch is working properly.
Not sure how valid a test it is, but something to consider”
See http://www.aulro.com/afvb/discovery-...le-causes.html for more details.


Common causes switch issues – Air conditioning water leaking onto it. See the link below on the repair routine.

Remedies
XYZ Inhibitor Switch Repair
http://www.aulro.com/afvb/projects-t...uhb100190.html

Redirect or lengthen the air conditioning tubes
http://www.aulro.com/afvb/discovery-...n-hoses-c.html



Gear Selector
Moving the gear selector too quickly (for example the car was in D whilst trying to start it and the driver moved it into P to get it to start) will provide signals that the transmission ECU will not understand, causing it to go into ‘limp home’ mode.

Remedies
Either a stop and restart of operations via the ignition switch or a reset of the fault code via the OBD will rectify this cause.
Slow down your behaviour with regards to gear selection.



Wiring Harness
Several reports about wiring connectors or damage to the wiring harness.
The energiser wire to the Starter solenoid (the thin green wire) has been reported as a problem. Loose oily connection.

Some have reported wires rubbing on the top off the gearbox and shorting together.

See http://www.aulro.com/afvb/discovery-...le-causes.html for more details.

Remedy
Pretty obvious, but fix the faulty wiring....

Low Fluid Level
Low fluid level in the auto has been reported to cause the M&S lights to illuminate. See http://www.aulro.com/afvb/discovery-...le-causes.html for more details.

Remedy
Check the fluid level and top up, if required.
Follow the workshop manual on procedures to follow.

http://www.aulro.com/afvb/discovery-...oil-level.html may assist.


From the Workshop Manual
There are 18 listed reasons in the workshop manual why the M&S lights come. Sure, the gear position switch (also called the w,x,y,z switch in RAVE) is first on the list, but there are other reasons. Just because the symptoms seem to be the same as others have listed on AULRO, doesn’t mean that the fault is the same, unless ALL of them match.

See RAVE for more details. Available from the AULRO shop, if you don’t have one.

From RAVE
The existence of an intermediate state (on the W,X,Y,Z switch)causes a fault code to be detected by the BCU. To reduce the chances of the fault condition occurring while changing selector lever position, the inputs are debounced and only considered valid when they have existed for at least 33 ms.

When a Fault is Detected
While the ignition is on, the electronic automatic transmission (EAT) ECU diagnoses the system for faults. The extent of the diagnostic capability at any particular time depends on the prevailing operating conditions, e.g. it is not possible to check torque converter lock-up while the vehicle is stationary, or to check for a short circuit to earth if the circuit concerned is already at a low potential. If a fault is detected, the EAT ECU immediately stores a fault code and the values of three operating parameters associated with the fault. Depending on the fault, there are four possible effects:

• The fault has little effect on gearbox operation or vehicle emissions. The driver will probably not notice any change and the warning lamps remain extinguished.
• The fault has little effect on gearbox operation but may effect vehicle emissions. On North American specification (NAS) vehicles, if the fault is detected on a second consecutive drive cycle, the MIL illuminates.
• All gears are available but kickdown does not function. The sport and manual warning lamps flash. The MIL remains extinguished.
• Limp home mode is selected and vehicle performance is greatly reduced. The sport and manual warning lamps flash. In all markets, if the fault is detected on a second consecutive drive cycle, the MIL illuminates.

After the detection of a fault, the effects remain active for the remainder of the drive cycle. In subsequent drive cycles, as soon as the EAT ECU diagnoses the fault is no longer present, it resumes normal control of the gearbox. The conditions required to diagnose that the fault is no longer present depend on the fault. Some faults require the engine to be started, others require only that the ignition is switched on. After a fault has not recurred for forty warm-up cycles, the fault is deleted from the EAT ECU memory. Only five different faults can be stored in the memory at any one time. If a further fault occurs, the fault with the lowest priority will be replaced by the new fault.




Mechanical limp home
In the mechanical limp home mode, gear engagement is controlled by the manual valve. The gearbox is fixed in 4th gear if the fault occurs while the vehicle is moving, or 3rd gear if the fault occurs while the vehicle is stationary. 3rd gear is also engaged if a vehicle is brought to a stop and the selector lever is moved out of, and back into, D. Neutral and reverse gear are also available.

CAN data bus failure
In the event of a CAN data bus failure any of the following symptoms may be observed:

• EAT defaults to reverse and 4th gear if the vehicle is moving, 3rd gear if the vehicle is stationary.
• Harsh gearshifts.
• Sport and manual warning lamps flash alternately.

I have had flashing M&S lights on two occasions since owning the D2. On the first it was on start up. The vehicle was in limp home and I am sure it was third gear.

Plugged in nanocom and it came up with fault "can bus timed out." Cleared fault and all was good.

On the second occasion I did not drive it. I just used nanocom, cleared the fault(which I think was the same) and all good. Last one was about four months ago and there was about twelve months between them.

I just put it down to computer gliches.