Error code 64 – Alternator FR Terminal System

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Error code 64 – Alternator FR Terminal System



First of all – what is it?



The FR signal (PIN 4 – Blue Wire) communicates to the ECU how "hard" the alternator is working to meet the electrical demands of the car, including charging the battery and any loads which aren’t monitored by other sensors. On newer cars this can be monitored and the cars ECU can actually switch off the alternator when it is not required.



This signal is a square wave that varies in pulse width according to the load on the alternator. The ECU puts a 5V (approximately) reference voltage on the wire. The voltage regulator will drop this signal to approximately 1.5V in proportion to the alternator load. Therefore, although it should seem that the alternator should send the signal to the ECU, it is after all designed to produce an electrical current; it is actually the ECU which sends a small voltage to the alternator.



If the electrical load is very high, (let's say you're also running a 5,000 watt stereo system) the FR signal will remain a constant 1.5V. That’s 100% duty cycle, so 1.5V is the lowest voltage you should ever be able to measure if the system is working and that is it working at full capacity.



On the other hand, if the load is very low, the FR signal can remain at a steady 5V. This tells the ECU that the battery is fully charged and the electrical demands are very low.



For all this to happen though the FR has first to SEND a constant signal for around 20 seconds to the ECU on start up, think of the lights on your dash which light up on start up as the ECU checks its systems and monitors its sensors. If your alternator isn’t running correctly at this time it may be that the ECU does not receive this signal. I am not sure if this means that it will not recognise the FR signal after this or how it reacts to it.



Why does it occur?



There are a few possible causes – an open circuit in the alternator FR circuit running from the alternator to the ECU (possible) – a problem with the ECU (less likely) – or a problem with your alternator itself (more likely)



How to test it then?



There appears to be two ways I have found.



Run the engine first until all of the lights on the dash have gone off then switch the engine off, keeping the cars ignition at “on”, then unplug the alternator. If you check on the loom plug you should find a voltage of between 4.8V and 5.2V being sent from the ECU. If you don’t have this there is either a fault with the ECU or a short circuit in the wiring from the ECU to the alternator.



If this is okay you need to plug it back in and check the alternator. The simple way is to insert a pin into the blue wire so you can attach a voltmeter and then let the engine run at idle, with nothing on that will consume large amounts of electricity, such as the radiator fans. Measure the voltage coming from the ECU to the alternator and it should be around 5V. Switch on the lights and the voltage regulator in the alternator should drop it to anything between 4.8V and 1.5V. If it drops to 1.5V with very little load on it, this would appear to be a sign that it is struggling to cope and is probably being stressed on a day to day basis.



Why do you want to know this?



If your alternator is struggling to cope it is believed that the ECU will not allow MIVEC to kick in and it is also a sign that you may have to start preparing for a new alternator.



Please feel free to add any other things you have noted about the FR Terminal system or to correct any of my points, especially if you have any knowledge of electronics or car control systems as I am just finding out as I go along!



Bill