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Hi! I'm new to this forum but have read quite a bit of it. Let me start with what a great forum this is, given the amount of information that is available. I had been interested in a volt for a long time but after seeing how much information is available with all these enthousiasts, from the web and service software available, I took the plunge on a risky volt... ;-) Always up for a challenge.

I have bought a second hand volt that is at this moment not driving (yet), with 214K kms out of warrant but for a very good price. Having some knowledge and experience with a Prius I knew that most of the HV parts do not really wear out, it's mostly software and sensors that fail that stop the car from driving.

When bought, the volt had a depleted 12V battery and several codes:

P1E00 - request MIL
P1FFF - service high voltage system
P0AA6 - Hybrid/EV Battery Voltage System Isolation Lost
P0ABB - Hybrid/EV Battery Voltage Sensor Circuit Performance
P0AFA - Hybrid/EV Battery System Voltage Low

I have since replaced the dead 12V battery with an 100 Ah 12v battery that seems to hold charge around 12-12.3. I have replaced the coolant sensor wiring and loom, reprogrammed the HPCM2 and BECM (not sure why the BECM needs reprogramming, is this the battery control module inside the battery pack?) using a VX nano dongle. (willing to write a howto by the way).

At first, when I reprogrammed the HPCM2, the ICE immediatley kicked into life after programming. A small victory as it seems the car can in fact run. ;-). I do believe it had a message 'propulsion reduced message' on its display.

After shutting down I however still had two errors in GDS2: P0ABB and P0AFA. When trying to power on the car I get the greyed out battery icon and 'power off' message in the console display. No way forward or backward, seems like its contactors are open.

P0AFA conditions (from the GM service manual):
The Hybrid Battery Pack Voltage is less than 205 V. OR The Minimum Hybrid Battery Cell Group Voltage in the hybrid battery is less than 2.05 V.

P0ABB conditions (from the GM service manual):
The hybrid powertrain control module 2 detects difference of 10 V between the average cell group voltage multiplied by 96 and the voltage measured at battery side of the main contactors.

So I went into GDS to verify some of these results. All of my battery cells are at exactly 3.85V, nicely balanced. Together with someone of a french Ampera site we estimate SoC to be at around 47%. This seems to be good news. If SoC is good, P1FFF is not triggered anymore, why doesn't the car move? :) At least we can discard the part of P0AFA: OR The Minimum Hybrid Battery Cell Group Voltage in the hybrid battery is less than 2.05 V.
We can also derive what the total battery pack voltage should be: 96*3,85 = 369,6 . A healthy voltage I would say!

I went back into GDS2 and checked the BECM data. Here we find the main problem, which is also noted by the P0AFA and P0ABB codes, the voltage of the battery at the main contactors is measured to be 140-160 volts (depending on the timing of my measurements, possibly related to the 12V battery going low). See the attachment with Battery Pack Data screenshot from the GDS2.

As such P0AFA's condition is met. Although my Cell voltage is great, nicely balanced and charged, my total EV battery pack voltage is way below the 205V treshold. (and also below the systems minimum 275V, why this value differs from the minimum value of P0AFA (205V) is not clear to me).

Also P0ABB is (of course) right: the average voltage of the cells multiplied (369,8) is more than 10V of of what is measured at the main contactors (140-160).

What's even more interesting is the BECM data with information regarding the voltage at the main terminals. Here we see that Terminal 1 is at 152V, whereas Terminal 2 is at 0V. I believe (need to check the service manual again) that these should also be at roughly the same values.

Some things that I need to figure out now:

-where is the main contactor voltage measured. Is it measured at the drive-motor-relay-junction? And if so at X5 (not likely as it is one connector), X3-X4 (the interlock connectors), or X1 and X2?

-why did the car start (twice actually) the ICE. Is contactor operation heavily influenced by how 'good' the 12V battery still is? I am assuming that the 100AH (but used..) 12V battery would have more than enough juice to operate these, it is normally used to crank a BMW X1 diesel.

-Where is the BECM located itself (in the battery enclosure?) I understand that this is key in my problem, as the BECM forwards it's fault codes to the HPCM2. I expect this to be done via X1 and X2 (they look like low voltage serial connectors), but not sure yet.


Hopefully my post will help out some people later on when their volts run out of warranty!
 

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What is the history of this car? (Why is is inoperative?) Car accident? Neglect?
 

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Discussion Starter #3 (Edited)
no damage whatsoever. Was traded in at an Opel (european GM) dealer i believe (but not deemed good enough as occasion as of mileage) and then sent to secondary market, where I bought it.

Apart from the typical wear and tear relating to its mileage, the car looks well maintained under bonnet and as it should. Problem is I do not know what exactly the 2nd hand car dealer (who had no knowledge of the volt or its working) did or tried apart from installing a different battery. The person who I bought it from thought it would have to start on the 12V battery (like a normal car), which at least explains why he would never get it to work.
 

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Discussion Starter #4 (Edited)
Additional information: when the car is now 'powered on' , the screen stays on 'power off' in the center console, but with the battery information on the center console vague and looking like the battery is fully charged, however just after the reprogramming of the HPCM2, I got the same view (power off) but with 2 green bars, assuming it has measured something (with contactors closed). PS mind you, the information is dutch, as I'm from The Netherlands.
 

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Discussion Starter #6
Not sure if capacity learn (I believe it is a function) will help in getting proper readings from the 'Terminal 1 and Terminal 2'.

Does anyone know where Terminal 1 and Terminal 2 voltages are measured and by which component? Will also review all grounds.
 

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What year Volt do you have? Have you checked the manual service disconnect? The manual service disconnect is located in the center console under the storage compartment. Remove the storage compartment and you should see the orange disconnect. Make sure its connected all the way. If its connected, then remove it and test the fuse for less then 10 ohms resistance. Just measure across the 2 contacts in the disconnect, the fuse is internal and not replaceable.
 

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Discussion Starter #8
MDS is correctly seated. Have checked resistance and that checks out as well.

Have cleared the P1FFF error (that came back although the sensor and wiring checked out correctly). Car won't charge and the EV battery is also slowly losing voltage (was 160V, now around 120-122V).

So perhaps although the individual cell voltages seem to be correct (3.84-3.85), the battery might indeed be depleted very far. If I would have a P0AFA and P0ABB error, would that prohibit charging?
battery-charger-error-with-cable-plugged-in.jpg

Will check the full wiring from connector to charger tomorrow. I did see at the 'contactors open' reasons, one fault regarding High Voltage Interlock. As I understand those are the high voltage (orange) wires that come from the top of the battery drive motor junction block relay.
high-voltage-interlock-circuit-fault.jpg
 
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