Smart charge and MOT

Q

I haven’t written before but I wondered if you might know the answer to the current situation with respect to the issuing of vehicle emissions results with the MOT certificate? I have received one of these for every certificate for some time now but was told by the tester of my car this week that they are no longer issued.

This is not a great problem of course so long as the car passes but I am always interested to see how the engine condition deteriorates over time and mileage and this is a really good annual way of seeing it. I have tried to find out online if there has been a recent change to the certification policy but cannot find anything relevant. Perhaps with your contacts you may be able to solve it?

Whilst writing I can’t resist asking if anyone can clear up the question of how the Ford Smart Charge system works in detail.

I have a 2011 1.6 Ecoboost Focus and it had a new battery four years ago. The Stop-start system stopped working some time ago and the run-on time for the radio reduced right down. I took it to be checked at a garage who said the battery was OK but needed charging. I did this and the system worked fine for a couple of weeks but was then back down to no Start-stop again.

Checking the voltage was 12.2V and another battery check said OK again but low on charge (alternator is working fine).

Car starts and runs perfectly. Looking online I can see other people with similar situations but no real answers. I understand the philosophy of the software for energy efficiency but cannot see why it would allow the voltage to drop so low.

I’ll leave these two thoughts with you and thanks again.

Steve Lukey

A

The MOT regulations have changed and a sheet showing emissions results does not need to be issued, in fact from the August 26, 2021 a pass certificate does not need to be issued. The gov.uk website states:

“The requirement to issue a paper VT20 pass certificate will now be optional. You may continue to issue a paper copy if you wish however there is not a requirement to do so, unless the customer makes a specific request to have one.

A paper VT30 fail certificate must always be issued, including those generated as part of a PRS. Customers can download and print certificates from the Check MOT history service. They will need the vehicle registration number and the 11-digit V5C reference number.”

To explain the smart-charge system it is probably easier to start with a normal charging system. This uses an alternator which has normally just two wires, the main battery feed and the control wire going to the ignition warning light. Providing a voltage is sensed at the main battery feed, the alternator will then put out a charge regulated by the speed of the alternator, and the internal regulator.

As soon as the alternator begins to spin it will pump out as much voltage as possible up to the set limit.

This causes a drain on the engines resources and so the smart-charging system was designed. This uses an alternator with an internal regulator, but which is controlled by the smart charge control unit (PCM). Any failure in the smart-charge system will normally default the charging back to 13.7 volts.

Ford were one of the first to adopt the smart-charge system, and there are now quite a few variations. This becomes even more complex with the introduction of hybrid vehicles and the Ford Smart Regenerative Charge System.

The general principle of the normal smart charge system is that by using an extra two control wires the alternator will sense the load and the condition of the engine. The alternator uses the main battery connection and a three-wire plug on the rear of the alternator. The threewire plug is connected as follows: Pin 1 = Alternator Feedback, Pin 2 = Alternator Load Request, Pin 3 = Reference Voltage.

When the vehicle is first started the control unit takes into consideration the engine coolant temperature, as well as the air intake temperature, and knows that the engine is cold. It will then boost the battery charge, pulling it back as it calculates the under-bonnet temperature coming up. It is often thought that the smart-charge system boosts the voltage only in response to load, but this is not strictly true.

The system is easily tested but will need a ’scope, as the fluctuations and wave forms need to be tested.

The basic checks are as follows:

Using a ’scope to test pin 1 – this is the feedback from the alternator and must show 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.

Testing pin 2 – this should show a square wave pattern that will change as the load request changes. Putting on the HRW, lights, etc, should show a change in this pattern. If there is not a change in the pattern this indicates that there is no request from the control module, and that would be where the fault lies.

Pin 3 – is the battery voltage and can be checked with a voltmeter.

As mentioned, the newer Regenerative Charge Systems get a little more complex, but the alternator still has the three control wires marked AS (Sence), RC (Gencom), LI (Genmon) and it tested in a similar way.

Ge Getting back to your personal situation, the battery charge rate and level will drop, if the smart-charge PCM is not operating correctly, as this will be too low to maintain the levels required for the vehicle and the battery.

You may need to find a garage who will be able to fully test and diagnose the fault using an oscilloscope.