ECU - Overcharging battery

mr socco

Have an overcharging problem with my car. While idle it's charging over 15 Volts. Car has had to be jumped a couple of times - presumably the overcharging is draining the battery. The mechanic changed alternator and battery and no change - still overcharging. He also said he's checked all possible cables etc.

Now says it's probably the ECU. Would a faulty ECU cause an overcharge? Know that an overcharge caused elsewhere could damage the ECU but just wondering if a faulty ECU could itself cause overcharge??

Nissan doctor

Car type?

TestTransmission

Nissan doctor wrote: »

Car type?

2003 Focus 1.6

Gophur

mr socco wrote: »

Have an overcharging problem with my car. While idle it's charging over 15 Volts. Car has had to be jumped a couple of times - presumably the overcharging is draining the battery. The mechanic changed alternator and battery and no change - still overcharging. He also said he's checked all possible cables etc.

Now says it's probably the ECU. Would a faulty ECU cause an overcharge? Know that an overcharge caused elsewhere could damage the ECU but just wondering if a faulty ECU could itself cause overcharge??

You need a new mechanic, the current one doesn't seem to know his arse from his elbow.

The ECU does not regulate the output of the alternator.

ZENER

Gophur wrote: »

You need a new mechanic, the current one doesn't seem to know his arse from his elbow.

The ECU does not regulate the output of the alternator.

Apparently on the Ford Focus there are 2 connections to the ECM. It's to do with "Smart Charging System" employed on these cars. The temperature of the intake air is used to regulate the charging system via the idle regulator.

Does the car throw any codes ? Get the mechanic to check for them. Is the car performing normally otherwise ? If the air intake temp probe was faulty it would impact on performance I would imagine. If the car behaves normally other than the charging issue then replacing the ECM may be the way to go !

Ken

Nissan doctor

Gophur wrote: »

You need a new mechanic, the current one doesn't seem to know his arse from his elbow.

The ECU does not regulate the output of the alternator.

Yes it does.

I had a feeling it would be a focus. I think ford can reprogram the ECU to solve the problem in some cases.

mr socco

Thanks for replies fellas. Yes (2003 Ford Focus), car is running fine apart from the overcharging. Flickering Engine Management Light (occasionally) and sometimes needles on temp gauge and fuel gauge twitch a bit when engine off. Fault came up as overcharging.

Mechanic going to get someone to reprogramme the ECU after checking everything possible (hope this is true), really hope this solves it.

P.S. is it possible to simply test if the overcharge is result of computer by disconnecting computer from alternator and see is the overcharge still happening??

Fishtits

You need a new mechanic, the current one doesn't seem to know his arse from his elbow.

The ECU does not regulate the output of the alternator.

You can't legislate for ignorance...

The Focus has what Ford call the Smart Charge system.

It involves sensors measuring air temp etc, the ecu sends signals to the alt demanding various charging outputs, the alt sends signals back to the ecu confirming said commands.

The problem areas are the voltage reg corrodes at its output terminal within the alternator, but 9 out of 10 cases are down to wiring loom failures, usually close to the alternator and due to vibration.

Some cases may require Ford software intervention to cancell the charging lamp

crosshair1

Disconnect 3 pin plug on alternator. This will force alternator to act conventionally, about 14v out. My money is on the alternator being chinas finest...

Gophur

Fishtits wrote: »

You can't legislate for ignorance...

.................

Thank you for the insult!

Read what I posted, "The ECU does not regulate the output of the alternator". The regulator regulates the output voltage. If there's 15V then the regulator is faulty. The ECU would never send a signal to a regulator to up it's output to 15V.

It seems some people do not understand what a regulator does.

Nissan doctor

Gophur wrote: »

Thank you for the insult!

Read what I posted, "The ECU does not regulate the output of the alternator". The regulator regulates the output voltage. If there's 15V then the regulator is faulty. The ECU would never send a signal to a regulator to up it's output to 15V.

It seems some people do not understand what a regulator does.

On smart charge systems, the regulator does what its told to by the ECU, if the ECU is faulty, as can be the case one these, it can send incorrect power requests to the alternator.

Gophur

Nissan doctor wrote: »

On smart charge systems, the regulator does what its told to by the ECU, if the ECU is faulty, as can be the case one these, it can send incorrect power requests to the alternator.

It may well send an incorrect signal but a properly functioning car voltage regulator is incapable of producing 15V. A voltage regulator will have circuitry preventing the output going over a pre-determined voltage. The only way the voltage goes high is if the regulator is damaged. Think about it? Why would the ECU ever send a signal to a voltage regulator that would kill itself? What system would allow such an error?


The alternator output needs regulation, to ensure it's output is rectified and the voltage stays between pre-determined limits. The current output of the device is another factor that needs control and, for this, definitely, the ECU can control the output.


Back to the OP, it is clear the mechanic does not know what he's at but is using the tried and tested method of replacing everything until the "problem" is fixed, at no cost to the mechanic but al all cost to the OP.

mr socco

Just an update for anyone interested. Cable was unplugged from the alternator and alternator was at the correct charge. So, basically cable to ECU and ECU are isolated. Bringing it to another mechanic who knows more about these things. Found some interesting info on the smart charge system in Ford (below). Apparently never supposed to jump start smart charge vehicle with a flat battery. Oops.




Ford Focus alternator smart charging



First things first, check the battery, not just condition, but correct type. A lead acid battery will not work properly with smart charge, it must be Silver Calcium! Easy to over look.



Next, put a meter across the battery. Remember when you remove the smart charge 3 pin plug from the back of the alternator, it reverts to a conventional alternator! If you do not have about 13.8 volts, carry out basic charging system checks and suspect the alternator, its not a smart charge fault !



Correct charge voltage from the alternator, then its time to start on the smart charge system, and you will need a scope. First the system.



Pin 1 = Alternator Feedback

Pin 2 = Alternator Load Request

Pin 3 = Reference Voltage



Now, pin3, must MATCH battery voltage ! Its fed from a fuse in the CJB, and a high resistance on the fuse contacts causes a volt drop, and the smart charge drops out !



Next pin 1 & 2 need checking back to the PCM for resistance, isolation from ground and each other. If ok, its out with the scope.



Pin 2 is the request from the PCM to the alternator. This will be a square wave pattern that will change with load request. So lights, screens etc on and monitor for a change in the pattern. (Obviously back probing with the plug connected)

No change in the pattern means no request from the PCM, you should now suspect a PCM fault. Correct pattern and move on.



Pin 1 is the feedback from the alternator and MUST remain a constant square wave pattern. If this pattern mirrors the one on pin 2, the smart charge part of the alternator is faulty, and a new unit is required.



With these simple checks, you should always be able to diagnose a smart charge fault.



Another point to add is, never, ever, jump start a Smart Charge vehicle with a flat battery.



The system can produce up to 18 volts, which can fry major modules.



The theory behind smart charge, is a battery will take a charges at its most efficient when it’s cold. Following start up, the PCM checks the Engine coolant temp, and intake air temp, and calculates a cold engine. It will then boost the battery charge, pulling it back as it calculates the under bonnet temp coming up. Its not there to compensate high demand as is the common misconception.



The problem comes on a jump start, when the PCM sees a cold engine, and then a poor battery condition, and can then instantly zap out about 18 volts because its trying to recover the battery. Unfortunately this sudden surge can cook modules.

Plug

When I got my focus there was a charging problem with it. The problem was a bad connection on the alternator with the three wired plug. I have never seen an ECU on these being replaced because of a charging problem but I have seen a few alternators. But that dosen't say just throw in an alternator and hope for the best:rolleyes:
If you hook it up to Ford IDS you can see the voltage output or duty cycle from the ECU to the alternator, if thats not there well then you may have a bigger problem.