Hi there. I recently replaced the alternator on my 2015 RDX. Voltage at the battery was around 11.6 while running before and went up to around 14.4 afterwards. I thought the problem was solved, but the “charging system malfunction” light keeps coming on. I have a cigarette lighter voltage reader, it came on while driving with a voltage of 14.35 which seemed normal to me. It came on again today at a stoplight at 13.84 volts. The alternator certainly seems like it’s working, but something isn’t right. Do I need another alternator? Could it be the tensioner? Any ideas are greatly appreciated.

 

There's nothing wrong with the alternator, it looks like it's the current sensor. But the correct thing to do is to read the DTS from the beginning.

 

The current sensor was also replaced recently. So it isn’t that. The light continues to come on when voltage seems to be what I would expect. Going 20-30 mph the charging malfunction pops up with 14 V. Where does one find the DTS? Would be nice to read through it. I’m starting to think the car doesn’t like this alternator though…

 

The cigarette voltage readers are very handy but they're not going to tell you everything about the alternator output. It's possible that the alternator voltage output is spiking at times and tripping the voltage output window limits. You would need a scope to look at the output signal for voltage spikes. Where did you get the alternator?

 

That's a valid point, it has been a useful reference but definitely not very precise. This was an Advance Auto alternator, so very possible that it's bad. I've heard that 1/3 from the autoparts stores are bad. Is the best way to go a remanufactured denso? I don't want to have to do this job more than twice...

 

I have a 2010 RDX, in addition to a 2016 RDX and I replaced the alternator using a Napa remanufactured alternator (not Denso), I wanted the Denso remanufactured one but they didn't have one in stock and I needed my car. Right after I put this alternator in it work okay as far as charging, but it was noisy, a really irritating whining sound. I returned it when they had a Denso in stock and all has been good since, a little more expensive but well worth it.

 

I did some more investigating and reset all of the codes to see what would come back. After driving for about 8 minutes the codes P16E2 and P16E3 both showed up. So communication with the PCM isn't working properly. Could this still be a bad alternator or is it more likely a bad PCM or wiring? Appreciate any input...

 

When you first had the charging problem did you scan for codes and have you seen these codes before? I think the PCM communicates to the batter sensor and alternator on a single wire (LIN network) so if the battery sensor or the alternator is bad it can possibly affect the single communication line, pull the line to ground or power and you lose communication and get the two codes, or the PCM or wiring may be the problem.
I don't know if this has been the problem all along or it started with either the batter sensor or alternator replacement, did you notice any differences in operation after replacing each of these items?


Some information about these two codes and what to check

 

Thanks for the video, that explains a bit. The new alternator made the battery voltage look correct, but the new battery sensor did not seem to help. So I put the old one back on and cleared the codes. Looks like I'm right back where I was in the beginning where either my replacement alternator is putting out too much juice and needs to be replaced, or the battery sensor still isn't right. Most likely suspect is that alternator though, I'm trying to source a Denso to replace it again.

 

RockAuto has denso alts available https://www.rockauto.com/en/moreinfo...9HbcCEiDoH8%3D

 

With the original battery sensor back in place have you driven the car long enough to check if the codes come back, or not? Might take two drive cycles but it would be good to see these codes gone to rule out the PCM as a possible problem.

 

Yes, it was the second drive cycle both of those codes came back on. What's the best way to diagnose the PCM being bad?

 

It would be best to put a scope on the PCM communication line to see what's going on but not feasible if you don't have a scope or wiring diagram. LIve data capture using a scanner may help some to see if there's any active signal control of the alternator, which I suspect there isn't because of the communication codes.
If the alternator and battery sensor do share the same PCM control communication line then either component could possibly be bad and shorting or loading down the communication line causing both codes, this assumes the PCM is good.
The challenge is, to find if either the alternator or the battery sensor is bad you have to remove or replace one at a time and do the drive cycles again to see which codes come back, I think you can remove the battery sensor from the communication line by unplugging the two pin connector and do the drives cycles to see which codes come back but not sure about unplugging the alternator and doing drive cycles, probably safest to replace with a known good one, which is a costly if it isn't the alternator. If both alternator and battery sensor check out good then the PCM or wiring from the PCM to the alternator and battery sensor are prime suspects. PCM's are typically very reliable and why I'd focus first on the alternator and sensor. This is kind of a tough one and I'm not sure I'm giving you the best advice, I'm hoping others can help you out more.
Going back to when the problem first started were you seeing a check engine light and if so is it similar to now with the communication codes?

 

Here's a Youtube video on how to diagnose the communication problem, most useful information starts around the 10:00 mark. He uses his scan tool scope to look at the LIN line, the single wire going to the alternator from the PCM. The expected voltage levels and what it looks like with and without the alternator connected. If the alternator or battery sensor is bad and pulling this LIN line high or low you would see this right away and if the PCM is good and you disconnect the bad alternator or battery sensor the LIN line signal would be restored to the correct voltage levels and waveform pattern. If the PCM is bad or the wiring is shorted to ground or power you'll still see a problem with the signal no matter if the alternator and batter sensor are disconnected. If you don't have a scope you might find a bad alternator or battery sensor by disconnecting one at a time, clear codes, do the drive cycles see what codes come back. If you see only one of the two codes come back after disconnecting the alternator or battery sensor then this means the PCM is communicating again with the component that's still connected and the component you disconnected is causing the problem and the PCM is good,

 

Extremely helpful response, thank you so much. I will see if my mechanic friend can get me access to a scope. Otherwise I will try to run the simple disconnecting test and see what codes show up. Already ordered a Denso alternator today, so if that's the problem I'll throw it in there.

 

I ended up putting the original current sensor back on the car since the new one made no change. By disconnecting the alternator and current sensor one at a time I was able to determine that indeed the alternator was causing both the codes to show up. I think the voltage regulator on the aftermarket alternator just wasn't doing it's job. Lots of people told me that could be the case and they were right. I replaced the Autozone alternator with a remanufactured Denso from RockAuto. That finally seems to have fixed my problem, hopefully for good. Thanks everyone for your help getting me on the right track.