Today I finally had the battery pack replaced. I remote started and restarted the truck multiple times before leaving the shop and all looked ok. As I was driving home about 20+ miles from the shop all seemed well. I was watching the battery temps from when I left and I started out in the mid to low 60 degrees and was in the 80's when I was getting closer to home. After I go toff the highway and made my way to my house on the side streets the battery temps went into the upper 80's and lower 90's. I made a stop at a store and used the remote start after my 2 minute stop and all was well. As I got less than a mile from my house the Check Engine light came on and I pulled the codes when I got into my driveway and sure enough it was the same codes for the battery fan not turning on. I cleared the codes and restarted the truck and drove a few blocks and shut off the truck and restarted it a couple of times and the codes came back.

I pulled the cover off of the battery pack when I was back in my driveway to verify the battery pack was replaced and I could clearly see that it was replaced with a new unit.

So now what do I do??? I don't know what else could be causing the fan not to turn on. Is there a module outside of the battery pack that needs to be looked at?

I need to find out how to fix this weird issue so I can safely drive this truck. If anyone has any input on this please let me know.

 

M so what are these codes that pop up? can you list them out? They are usually pretty accurate with some interpretation.

 

I see the same two DTC's after clearing them.

DTC P0AC4 says the Hybrid power control module has requested that the MIL light be activated.

DTC P0A81 says the battery pack cooling fan or circuit has a problem.

The entire battery pack was replaced so why could this still be happening? What external component could cause this to fail?

 

Monte I took a few minutes and read back through the thread. If this were mine giving this issue I would take the information from Jaime and run with it.
Quote "Yes, there is a relay for the fan inside the battery case. It is controlled by the battery control module (BECM) through the white wire with green stripe. From the relay, two terminals (2 and 3) both connect to the external connector on the Red wire with white stripe. From here it goes to 12V through the BECM FAN Fuse (15A) in the Aux Fuse Block. When the BECM commands the fan relay to turn on, it grounds the white/green wire connected to Terminal 1 of the relay. Power from the relay is provided to the fan through the pink/dark blue wire on Terminal 4 of the relay.

My interpretation is that the hybrid battery cooling fan power is coming from a 12V source at your fuse block either under the hood or in the dash and not internally from the hybrid battery itself!
To me that would mean that I have a fuse block issue or a wiring issue from fuse block to the relay inside the hybrid battery. I would be trying to locate a wiring diagram to trace the power source for the hybrid cooling fan. Maybe start by verifying power at the fuse block and then at the hybrid battery connection?

Some interesting internet info on the internet about GM fuse block issues they even mention the radio popping..........weirdly familiar from your post that mentioned that and some dash issue etc?

 

dnt1010 thank you for the info.

I can add the ground and see how it goes no problem there. I did not swap out my main fuse box but I did replace the positive and negative power cables. That includes the positive power cable that feeds both the main and aux fuse boxes.

The hybrid battery fan gets it's power from the smaller aux fuse box.See the Hybrid Battery _Battery Cooling PDF. I checked the fuses and they are good.I do not know if it's a two piece fuse box like the main one. That's something I can check as well.

I also attached the TSB from the ACDelco website for the DTCP0A81 error code and what troubleshooting steps they provide for that and I also attached the other more general Power Ground and Data wiring diagram for the hybrid battery pack that shows the 2nd BECM fuse in the aux fuse box.

 

You have some great data there. I am sure that you will find the issue soon. Hopefully an easy fix once you find it. Intermittent issues can be hard to find.

 

So I'm still dealing with this issue but I have some new updates. The other day I was checking the power that was coming from the AUX fuse box. Fuse 10 goes to pin 1 on the connector between the truck and the hybrid battery pack and I measured 12+ volts there on both sides of the connector and when I pull fuse 10 from the AUX fuse box I lose power. That is the power feed for the hybrid computer module. Then I checked the power for the fan. Power comes from fuse 2 from the AUX fuse box and goes to pin 11 on the connector and I had 12+ volts on both sides of the connector however I did not have any fan movement.

Next I removed the battery cover and I checked the connector going to the fan and the relay is impossible to get to with the battery installed in the truck. I could only touch it with my finger tips so I couldn't really check the relay too much. I put the safety plugs back into the battery pack and I stared the truck and holy cow the fan starts to work all by itself. I wiggle the fan connector and it stayed working. I took a small stick and I poked the relay a bunch of times and the fan stayed working. At this point I figured they had a lose connection on the new battery pack so I was good to go and I put everything back together and the fan worked as it should... Well it did for almost 5 days.

Now the fan is not coming on again and the same two codes are back. So today I tested for power again on pins 1 and 11 to see if I have 12 + volts going into the hybrid connector. Well now I see something different. On pin 1 for the power going to the hybrid computer I measure 12 volts with the key on and around 14 volts when the truck is running. Great!

When I measure pin 11 for the fan now I'm seeing less than 9 volts with the key on and just over 10 volts with the truck running. Here's two more interesting things I noticed. If I disconnect the truck's wiring harness from the hybrid battery pack my voltage on pin 11 jumps up to 12 volts and when I reconnect it to the hybrid batter pack it goes back down to 10 volts or less. The second thing I noticed was when the fan is suppose to come on the voltage on pin 11 drops to .7 of a volt and then the DTC's come on. I can clear the DTC's and repeat this process over and over and I see it drop from 10 volts down to .7 volts and the DTC's come on again.

As far as I know I have good power going into the hybrid batter pack to run the fan. What it seems like is the battery pack is messing with my power and it's not allowing the fan to work correctly. What I wish I knew was what did the power on pin 11 look like when the fan was working and going on and off as needed. Was it working off of the lower voltages or was it keeping 12-14 volts at all times and allowing the fan to work.

Can anyone explain why I'm loosing voltage on pin 11 to the fan when I connect the wiring harness? Seems weird to see the voltage drop like that.

 

I think you just solved it! Intermittent high resistance between the fuse box and the connector at the battery. When the fan is supposed to be On, the relay coil is grounded by the battery module.This pulls down that whole section of the circuit towards ground, through the relay coil. Reason the voltage goes up when you disconnect and goes down when you connect is that there is some load on the circuit from the battery module when it is connected, even if the fan is not commanded to turn on. This small load is enough to bring the voltage down slightly because of the high resistance further up in the circuit.

Now to test it temporarily, see if you can supply +12V directly to the fan relay. I think connecting new wires to relay terminals 2 and 3 directly would work. Run this wire all the way to the fuse box, or to a separate fuse directly to the battery.
Permanent fix would be to follow the wire all the way to the fuse box and inspect all the connections. Replace wiring or connector contacts as necessary.

 

If I could get into the battery pack deep enough to reach the relay I could try and do those things however It's just not possible they way things are put together. Only removing the battery pack or the middle row seats so I could remove the side panel on the battery pack would allow me to get to the relay and do all of that work. Also it's too cold outside now to be spending that much time outside. I do not have access to a heated garage.

Just to verify I'm hearing you correctly. Do you believe the power coming from the fuse box to the pin 11 on the connector to supply power to the fan is the cause of the high resistance when connected? If so it would be much easier for me to supply a new voltage source to pin 11 to run the fan. I could do that in a few minutes and allow me to run the truck normally again for the winter and in the spring I could do more to make a permanent fix when the weather is better outside.

 

Assuming the cause of the high resistance is further up the line and not at the battery connector (X350), then you could cut the wire (Pink?) going to Pin 11 and splice to the remaining bit of wire at the connector. Be sure to remove the 15A fuse in the Aux fuse box so that the cut wire wont be energized. I would recommend going straight to the battery through a 15A fuse (put fuse as close to battery as possible) and run the wire to the HV battery and splice to the Pin 11 wire. What did you have in mind for voltage source? Have to be careful not to connect to another fused voltage source that may be overloaded when the fan is running. That's why I recommend going straight to the battery. If you can find a location in the Aux fuse box to join to, that could work as well. Be sure NOT to use a wire gauge smaller than what's already there. From what I could find, the pink wire to Pin 11 is only 22 AWG and further up the line, the red/white wire is 18AWG. I'd use 16 AWG or larger for the whole run.