Peugeot Partner B9 Alternator LIN fault

Peugeot Partner (B9) 1.6L HDI (9HP) 2012

After a routine service, the diagnostic review revealed a fault present in the engine ECM.
U1401: Alternator LIN network : Registering of a fault on the slave node of the alternator LIN network.
There was no MIL on and the vehicle had suffered no apparent faults.

The first thing I did is verified the charge status of the vehicle.

9HP Alternator charge status

As you can see, in the image above, the alternator appears to be operating perfectly okay. This lead me to evaluate the LIN bus control circuit, as this is what the fault code mentions.
The service information suggests ‘suspect areas’ as; LIN / Engine management ECU / Alternator. That’s about all you get.

The Alternator has a single wire (LIN) connection with the engine ECU, and of course a battery charge cable (BAT+).

I connected the scope up to the LIN terminal, using a ‘breakout’ cable. I unplugged the connector from the alternator to see if the LIN bus was present, from the engine ECM.

Alternator LIN bus command signal

You can see that when I switched on the ignition, the LIN bus started. This proved that the LIN was generated by the ECM. But in addition, whilst the circuit was open, the signal was normal. When I then plugged in the connector the LIN bus changed. Notice the amplitude rise in the max voltage, coupled with the reduction in low level voltage.
You can also see a very small rise in command signal current, as indicated by the Green channel, (not as much as it should be. It should be around 10mA peak).

This outcome lead me to test the output from the alternator direct.

Alternator direct output (LIN circuit)

You can see that when I connected the scope to the terminal on the alternator, a signal shot up to 11.1 volts. There should be nothing present, as far as I know. This appears to be the fault with the alternator. Wouldn’t it be nice if the manufacturer’s service information could tell you this kind of information?

I then applied a load, via a test light, to the voltage signal and it collapsed to ground, as you can see.

Engine running Alternator output voltage load tested

This alternator needs replacing. That’s not happening just yet, as it’s working just fine from a end user position. But as soon as I get a chance to sample a known good one, I will post it here.

I have managed to find a vehicle with the same set-up, to sample for reference.
The first thing I did, (not shown here), is test for any voltage directly from the alternator LIN terminal. As I expected, there was no voltage output.

I then coupled up my ‘breakout’ harness and connected the scope as before.

Alternator LIN bus control and charging GOOD

Notice how the LIN bus current signal is considerably different from the previous images.
The next image is a close up of the LIN. You can see how the ‘Bi-directional’ control is illustrated by the current signal. It’s only a shame I didn’t take a high resolution capture, but sometimes you just have to use what you have.

Alternator LIN bus

Due to the orientation of the current clamp, I can deduce that the positive current ramps, just under 10mA peak, are due to the alternator’s control. The smaller negative current ramps, are from the ECM control. Because the voltage signal is provided by the ECM, there is very little effort required to switch the signal low, whereas the Alternator control has to pull the signal low.

Maybe I’ll get a chance to take a high resolution capture, when I have more time available.

As a note against the findings in this case, I happened to sample a similar fault on a Renault vehicle, that also uses a LIN controlled alternator. The vehicle had a LIN/alternator circuit fault recorded and was a permanent fault.

I tested the circuit, only to find a bad wire in the harness. I noted that in this case, the alternator LIN terminal, did provide approximately 12v directly. This made me think maybe there were 2 faults with this vehicle. When I repaired the wire and regained LIN date correctly at the alternator, all was well! No faults presented after the repair. Just goes to show; ‘Don’t jump to conclusions’