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I am having a peculiar problem in my 2007 4wd Scorpio .
Every time I switch on the ignition key I get all the indicators on the dash panel except the ecu engine sign , the engine will not start after cranking in this condition.
On switching the key on and off a couple of times the ecu sign comes on and the engine starts instantly and the car works perfectly.
I took the car to the milestone service centre and was told that the ecu and wiring loom would have to be changed at a cost of 75,000.
I took the car back and got it checked for wiring defects at a private garage ,who did a thorough job and could not find any faults .
I am using the car in this condition and am afraid that it may give up at anytime if the problem is not addressed .
The scanner has not indicted any errors .
I would like to have a feedback from any readers who have faced similar problems .

If the problem can be replicated reliably, ask the ASC to try plugging in a different ECU (you can also do this at a FNG if you have another car with the same model). If the problem goes away, go for ECU replacement only. If the problem occurs on the replacement (temporary) ECU as well, go for a loom change/ get it checked again.

Other possibilities are:
1. Bad key-mechanism.
2. Security system interference.
3. ECU waiting for feedback from some other component which is failing.

I have taken the car to the mahendra nbs service centre and they have replaced the key mechanism but the same problem persists .
security system has also been checked .
They are reluctant to try another ecu as they feel it may get damaged due to faulty. wiring
so i have been asked to replace both at the same time
i am reluctant as i feel they are not sure of the fault .
Now i have decided to go to some ecu repairers at kurla and try my luck .

Dont let the so called ECU repairers lay their hands on the ECU unless you are sure of the problem. Else maybe a properly functioning ECU could be conked by improperly trained hands. Though I dont have a solution for your problem, all I want to say is dont try to fix something whose condition is unsure. Speaking in general, it could be a loose wire, wherein the ECU is not receiving power. Hence no life to engine when cranked, and no CEL light which is again controlled by the ECU.

Also, did the Mahindra mechanics read out ECU data to know what the status of the ECU was when the CEL did not come on?

Absolutely right. The service guys are not applying their mind AT ALL. The 'ECU repairers' know even less, if at all, about the subject.

This is a transient problem caused most likely by ...
The problem would be most likely a loose connection to a sensor which is delaying the ECU from declaring 'All is well'. ECU checks the health status of some sensors on start up (key in ON position). Some of these sensors are absolutely essential, and some not, for allowing the injection sequence to start (crank the engine). In this case, the ECU must be waiting for a very long time for confirmation of the same.

Ultimately it will annunciate what is wrong, either via flashing that lamp to indicate error condition, or at least by recording the fault in internal fault memory. Looks like neither you nor the service guys waited that long. If checked with a Diagnostic equipment (OBD2 analyzer) the service guys will be able to isolate the faulty connection.

IF an ECU has to fail, it will not be intermittent. It will refuse to go on at all, ever. In your case you are able to start in one out of n tries - but it starts.

Unless there is a major problem with the harness loom due to fire or rats or accident, the loom never needs to be replaced.

If you are not able to get the service guys to use the diagnostic equipment, perhaps you can get together with @HimuraKenshin. He is (I think) in Mumbai, and has a scanning tool that you can connect and check if there are any faults recorded in the ECU.

DerAlte, just for my knowledge, which could be these essential sensors? Is it something like the crankshaft position or camshaft position sensors? Also, does the CEL come on at key "ON" only to indicate everything is fine? I had thought it would be a lamp test, and in the background the ECU would be running a self check.

Also, in such a case running a scan tool is the best option IMO. Not sure why the mahindra folks did not do(or did not reason out) so.

Hello magneto

Get the central locking checked , its the problem with central locking mechanism which is giving the issue . Central locking has the mechanism to disable the car start , my relatives had the same problem in their scorpio at times . Get it totally disabled or get it changed with new central locking to check and i am sure the problem will go away .

Could CEL lamp in dash or connecting wires itself be faulty? Resulting in incomplete loop.

-bj

That wouldnt prevent engine start.

The central lock issue seems to be interesting. Does this central locking system immobilise engine by cutting power to ECU? If yes, then the culprit may have been found.

Yes, and a lot of others - too many to list.

It stays on for the duration that the preliminary checks are conducted. Checks continue even after crank. "Everything is fine" = lamp not lit! Lamp flashing = "Fault".

Your guess is as good as mine! :) The obvious reason is that they are not trained to use their brains, nor to follow 'analysis with a decision tree'. Most service guys try really hard to appear as experts without the commensurate processes and knowledge to back them up. Come to think of it - this is a national malady, not limited to automobile service. To the point that most of us lack courage to honestly say "No, I don't know. Let me find out!"

The lamp check is a virtual check - if it doesn't light up for a couple of seconds at start, either the lamp or the wiring is faulty. The ECU doesn't reckon with this, the driver has to.

That IS the 'immobilizer' function. However, it doesn't 'cut power to ECU' - how will the ECU function to check immobilizer state otherwise? The ECU prevents cranking till immobilizer says OK.

In both my cars, or Maruti cars in general, CEL light remains ON as long as engine is not cranked. It switches off once engine is running. The manual mentions there will be an issue if this light turns on while engine is on. In the ON position, it is done to verify that the lights are functioning.

:Frustrati Guess we must now have qualified engineers in service centers, in order to handle the higher amount of sophistication found in newer cars. Come to think of it, manufacturers employ well educated graduates in R&D and they churn out such products. And when they develop problems, repairs are attempted by mechanics, who have much basic knowledge about the working. Yes some mechanics are masters by experience but that is mostly related to mechanical stuff and not ECUs and the like.

Sir, if the immobiliser was a part of the central locking system, as said by the previous posts, I do not understand why the ECU would have to check immobiliser. The logic you stated is correct for cars which have a factory fitted immobiliser. Both my cars behave this way. If I use a wrong key, the immobiliser light will blink, and the car wont fire up on cranking. This is done by the ECU based on the signal from the key detector.

Suppose an after-market immobiliser was used, which came along with the central locking system, it should use a crude method to immobilise the engine, either by disabling the starter or preventing engine firing, ie to start. So, when wiring the central locking, I think they have made the central locking system control power to ECU. I feel it is done this way. At least going by the fact that another member has come across the same problem.

Trained resources, not necessarily 'engineers'. Even a Diploma in Mechanical or Electrical will do wonders if they are trained on disciplined systematic analysis when troubleshooting. Without this, most self-taught mechanics in service operations of even good car companies just speculate and flap their mouths.

The problem is the A.S.S. ops in almost all companies do not look beyond their noses. They do train people, but don't follow-up on actual service operation for adequacy of resources and knowledge. For example, there are plenty of MUL-trained service guys who set up their own independent shops after a couple of years of experience in an A.S.S. operation. Is that monitored and replenished. Nope! What is left in most places is locally recruited mechanics who then proceed to learn by sight, and pretend to be experts.

The ECU waits on a permittance from the Immobilizer. If there is no separate Chassis Electronics module, the Immobilizer is implemented in the Injection ECU. In that case the ECU waits on permittance signal from key detector. This is the most common implementation in bikes with ECU-controlled injection.

I don't know anything about aftermarket central locking with immobilizers, but ECU power is straight from battery, and you can't access the loom to splice in a control element into that line, nor does it make any sense to do it.

It is simpler for aftermarket central locking to disable some other control element such as starter or ignition signal (read by the ECU). 20 years back Autocop used to do something like that (I don't recollect the splicing point), and boy it used to be a nuisance when Autocop would malfunction.

I think they might be doing it now too. I have seen a lot of Central locking systems, the premium models offering engine immobiliser feature. Just that nowadays with more manufacturers offering Coded Keys, such premium versions are no longer in demand. In case Mahindra had(at that time, ie 2007) adopted such a system, perhaps that would be the problem right?

Hi boys , I am an electronic and auto guy myself but not knoledgeable about ecu and car computers .
My car was at the nbs repair shop and they have checked the wiring harness and all the parameters on the scanner and nothing seems to be wrong ,ie no error codes .
I suggested to them that they can put in a spare ecu and check if the problem is sorted out ,but they have flatly refused citing the possibility of blowing their ecu in case of some major error in the wiring .
On the otherhand they claim that they fitted my ecu on another working car and faced the same issue .
So they claim that the ecu is the culprit .
So I agreed to replace the ecu at a cost of app Rs 40,000 , but that's not enough for them
They say it is company policy to change the front wiring harness whenever a new ecu is fitted.
Secondly you cannot buy a ecu from them or the market because the company claims that they get it in a blank condition and have to register car details on the computer like injector numbers chassis no and engine number to make it functional .
I am really not sure about the fact of their actually fitting my ecu on a another car .
I will be grateful if I can lay my hands on a socket diagram of the ecu so I can check some things I myself on a oscilloscope

you are saying that, its cranking but not starting??