LIN Bus decoder & LIN Controlled Alternators

[Alex@Van's]

Ben, thanks for this excellent article.

I have a weird LIN problem, and I hope you might be able to offer some insight.
Alternator #0 125 716 009
Regulator #0 272 223 024 (Transpo #IB3024)
2019-2020 USA Jetta

We're a rotating electrical rebuild shop, but we almost exclusively service American industrial and commercial vehicles, plus antiques. We repaired the alternator by replacing the regulator and rectifier, and returned the unit to service. 3 miles from the repair shop that removed and reinstalled the alternator, the battery light illuminated on the dash. Cycling the ignition cleared the light and it did not return, but the customer requested further testing and analysis.

When I mount the alternator to our Jimco test bench and connect our LIN V1 control box #TC-COM2, it initially responds to voltage setpoint commands, but then oscillates between the default setpoint and the commanded setpoint--15.3V for 1-2 seconds, then 14.2V for 2-3 seconds, back and forth. Jimco's technician speculated that the regulator is of a later LIN protocol version, which could yield unpredictable results, but they could not say for sure. My only option is to order in another voltage regulator because we can't currently afford to buy in a later version LIN protocol controller.

Can a LIN protocol version mismatch cause this? I will return to post results after replacing the regulator.

When we are in the market for new test equipment, I will reach out to Pico's Texas USA office for quotation.

Thank you!

[ben.martins]

Hi Alex,

Thank you for the feedback. As long as the articles we put out there are useful then its worth spending the time putting them together.

With regards to your concern with the Jetta. It may be that there is nothing wrong with the alternator as some vehicles may require a road test before the light will go out. If the light is out, the vehicle is charging and there are no fault codes it is likely everything is OK.

If you are testing using a LIN 1.X controller as the master and the alternator is a LIN 2.X slave, this may cause some issues. Whilst a master can be a higher LIN version than the slaves, I think problems can occur when the slave is higher. Typically they a can all exist quite happily together but the move from LIN 1.3 to LIN 2.0 was quite a big one with the introduction of enhanced checksum, larger signal sizes (up to 8 bytes) along with other enhancements. This may be the reason for your data to look a little unpredictable if your master controller is LIN1.X and you're trying to communicate with a LIN2.X alternator.

If you do decide to purchase Pico, then the LIN decoder will allow you to see the difference. The best way to see if the master is looking for a LIN2.X communication is to disconnect the alternator and decode the signal from the master. Be aware of additional slaves on the network as they may show additional ID's in the decode table. If possible make sure only the master is on the network. As enhanced checksum was only introduced in LIN 2.0, then if you have this present in the decoded data you can be confident it's a LIN2.0 protocol version. If not, then it's most likely to still be on LIN 1.X.

I hope this helps and please let us know how you get on.

Kind regards

Ben

[Alex@Van's]

Hey, just dropping in to let you know that I didn't forget about you. UPS lost the replacement regulator--and they are actually kind of rare, at least in the US. Regitar has stock but Transpo is backordered, no ETA. I expect #3 before the week is out. I can't believe the customer isn't beating my door down!

See you in a couple days.

[Alex@Van's]

The replacement voltage regulator exhibited the same behavior, oscillating between failover/default (13.9-14.2V) and LIN 1.0 setpoint (14.1/14.6/15.3V) at irregular intervals. Varying the load had no effect. Both regulators are Transpo #IB3024, but I don't see any reason to expect different behavior from a Regitar etc. I think we can say with a moderate degree of certainty that LIN 1.0 setpoint signals sent to later LIN version regulators are activate intermittently, and as long as the oscillation does not occur with no regulator connection, the regulator is most likely good.

It remains to be seen if the battery MIL is triggered. If it illuminates once, we will assume it is a system test following battery disconnection. If it illuminates more than once, I will return to post updates.

Thanks!

[ben.martins]

Hey Alex,

Thanks for the update and apologies for the delayed reply.

I think it is a case of the this vehicle needs to be driven to determine what happens next. If this is almost a characteristic of this regulator, then we won't be able to ever fix that!

As I mentioned in a previous post it maybe the vehicle needs to be driven for a bit and then reassessed. If a fault persists then we need to look further. If it's all OK, no fault codes and is charging the 12V battery, I think we can be more confident in releasing the vehicle back to the customer.

Keep us posted!

Kind regards

Ben