OBD2 code P1246 on Ford Focus 2. Fix it yourself

The battery charging system on the Ford Focus II rarely fails. As a rule, the main sign of malfunction is a voltage drop at the output from the alternator or at the output from the engine control unit. All this is accompanied by a burning alarm lamp on the dashboard (with the image of the battery), and when scanning the system pops up error P1246, the failure of the input load circuit of the alternator. Let’s deal with the error on the Ford Focus 2 together.

What caused the error P1246 on the Focus Mk2, checking

The first thing that comes to mind after decoding the fault code is a problem with the alternator. It is easy to check it. It should output its legal minimum 13.8 V without load, and if you turn on all the consumers on board, the voltage can drop to 13.6 V.

I don’t think I need to explain how to check the alternator. Take a multimeter and take the voltage from the alternator fuse. It is located here and it should have a constant voltage from the battery.

P1246: causes and checking

Now we are trying to get to the connector of the alternator itself. It’s not easy to do, but you can if you want to. There are three pins on the terminal. 

On one of them there is constant power from the battery, on the second the control signal of the alternator, and on the third one the output voltage of the voltage regulator is output. Let’s look at the schematic.

And we see that two wires go to the electronic control unit. These are the generator control pulses and the battery charge control pulses. We will check them first of all. We test the wires with a tester, but first we need to get to the ECU.

The control unit is located between the left front wheel and the bumper and to get there you need to remove the underlip on the left side. The location is not the best because the body of the unit often suffers from moisture and damage.

Just in case, catalog number of the electronic control module is Ford LQ-FKS-134, catalog number of the cover is Ford LQ-FKS-135. Ford control unit part number 1 712 930.

Now check the wires from the ECU to the alternator. Exclude contact oxidation, breaks, insulation damage, burning and other suspicious phenomena. If possible, it is advisable to check the wires with an oscilloscope. At least the oscillogram should look like this.

На графіку показано три канали:

1. The red channel is the output from the voltage regulator, its rating is about 5-7 V.
2. The blue channel is the voltage regulator control signal.
3. The green channel is just the voltage, due to which the error P1246 appears. More precisely, due to its absence.

Here is a graph is taken from the car with code P1246.

As you can see, the green channel has dropped well below the nominal voltage, that’s why the battery discharge light came on, that’s why fault P1246 was displayed. This signal also affected the second channel, which controls the regulator, which means that the voltage regulator is not working properly. Consequently, the problem is exactly in the supply wire, which goes through the fuse.

Fixing P1246 in Focus 2

To get to the underhood mounting block, remove the battery and disassemble the fuse box. It will not come off until we release the wiring harnesses, fastened with plastic ties, cut them off.

Disassemble the fuse box and study it carefully from the back side.

As you can see, in our case the lower power supply platform is oxidized. It could be burned or just covered with oxide. The red wire goes to the fuse. Generally speaking, the fuse box housing must be replaced for such corrosion damage.

However, if replacing the mounting block is not in our plans, we can simply move the fuse to a free place, making sure that it has not been corroded.

And so that the plate does not oxidize anymore, we apply a special insulating grease over the wire. In this way, you can defeat error P1246 on Ford Focus 2 quickly and without any help.