LIN a poor mans version of CAN.

Tales for this month....
​Recently we have had calls from Garages with charging problems on various brands.
 
Case Study 1.   A Ford  Focus Tdci 2016 came in with a charging problem, and after some preliminary checks the garage decided the Alternator was faulty and a  genuine replacement was fitted.
 
Codes cleared and retested, but the Charge system still showing a fault and not charging.
 
This system Is a LIN controlled Alternator, Single wire control. As the garage has no experience with this system the help line was called for help.
 
After a little research it is showing the Circuit for the LIN has 3 items present  the Alternator, PCM and the Active grill. So time for the Picoscope to come out.
 
As LIN is a single wire 12 volt based network and we know what the signal should look like, we sent the garage a waveform for their reference, And  the signal they had was not as expected. Below is a good LIN signal taken from file.

​A normal LIN signal ranges between 10 volts and 2 volts  (Ranging between  80% to 20% of a 12 volt signal).
 
As the alternator was already replaced we applied our attention on the other components on the LIN network. On closer inspection the connection at the Grill shutter motor we found severe corrosion and water ingress. On disconnection the LIN Signal returned as expected at the alternator and the charge rate was back to normal. This was not the first time we have seen this problem on a Ford Focus.
On some vehicles this LIN circuit will also include the the IBS (Intelligent battery sensor) to monitor the battery state for stop start systems and alternator feed back.
 
And as manufactures are using LIN as a cheaper alternative network solution we will be seeing more of these problems, considering it only has a single wire to communicate. So any fault on this circuit will cause total failure. 
We typically have calls on the help line every week relating to LIN problems, many relating to Window systems, this is a popular use for LIN and the controllers are exposed to water ingress with in the door modules on various brands and models.
 
Yet again we come back to the same conclusions that a scope as an essential tool for modern diagnostics, even for something a simple as a charging fault.