braveheartwallace
TYF Newbie
- Joined
- Dec 21, 2017
- Posts
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Hello everyone,
I drive a 2009 Hybrid Tahoe. About six months ago, I replaced the high-voltage hybrid battery, and since then (5k ish miles), I haven’t had any check engine lights or issues. Today, I drove from San Antonio to Pecos, Texas, a trip of about four hours. The car ran perfectly the entire time....
Toward the end of the trip, I knew I was cutting it close on fuel, but I had a jerry can in the trunk, so I decided to push on from Fort Stockton to Pecos. I was maintaining about 90 mph until I had to slow down to 60 mph behind a semi. I eased off the gas, letting the regenerative braking handle the slowdown.
At that point, I noticed the fuel gauge, which was close to “E” but not fully empty, suddenly dropped to empty. The fuel light came on, and the engine died. I shifted into neutral and managed to restart the engine. Knowing I was critically low on fuel, I stayed behind the semi at 60 mph for the last mile. Then, the engine died again, but I was able to coast off the highway directly to a gas station and stop at the pump.
At the pump, I filled the 24 gallon tank with 25.59 gallons and restarted the car, but it died again after about 30 seconds. Suspecting air or vapor in the fuel rail, I purged it using the Schrader valve under the hood. Initially, some fuel vapor came out, followed by steady gasoline. Thinking I’d cleared the air, I restarted the car and let it idle. It ran perfectly for five minutes.
I then drove a couple of minutes down the road, but it died again. I shifted into neutral, restarted it a few times, and managed to reach another gas station. There, I pulled over for more diagnostics.
The car showed no check engine light or trouble codes. The only issue was that it would idle for about 30 seconds before shutting off. Each time it started, it ran smoothly—no misfires, no hesitation. It would start, idle smoothly, and even rev up without issue, but it always shut down after roughly 30 seconds.
I called a mechanic in Pecos, and based on the symptoms, we both suspected a fuel system issue. When I tried starting it again, the car surprisingly ran long enough for a five-minute drive to his shop. Once there, it idled smoothly for 10-15 minutes while we examined it, but it eventually died again and displayed a “service power steering” message on the dash.
After that, we tried restarting it multiple times. It would run for about 30 seconds before shutting off each time, always running smoothly while it lasted. Using his more advanced scan tool (Snap-on), we finally pulled a trouble code: P0563 - System Voltage High.
This code hadn’t appeared on my earlier scans or triggered a check engine light. According to a GM technical bulletin for hybrid Tahoes, this code occurs when the ignition system voltage exceeds 18 volts for either six seconds or six times per second (not entirely clear which). We were able to clear the code a few times, but it kept coming back, and the car still wouldn’t idle for longer than 30 seconds.
I then had the car towed from the independent mechanic in Pecos to a Chevy/GMC dealer in Monahans. We will hopefully dive into the car tomorrow.
…
Just to provide additional context of my understanding of the General Motors two mode hybrid, the hybrid system in this vehicle operates at around 300 volts, while the air conditioner and electric power steering runs at 48 volts. All other standard car accessories, including the ignition coils, rely on the 12-14 volt system.
The DTC P0563 refers to the ignition voltage exceeding 18 volts, and I’m wondering if this could be related to the regenerative braking. When I slowed from 90 mph to 60 mph using regenerative braking, could that have caused an overcharge? After four hours of highway driving, the hybrid battery should have been fully charged.
The question is how an overvoltage could occur in the 14-volt system, which powers the ignition coils. Neither the instrument panel nor the Snap-on scanner showed anything abnormal. The dashboard consistently displayed 12-14 volts for the 12-volt system, and the Snap-on tool showed a maximum of 14.6 volts. Similarly, the hybrid high-voltage battery stayed within expected limits, peaking at 330 volts during my observations. From what I’ve read, some technicians report seeing up to 400 volts during regenerative braking, so this seems normal.
The P0563 trouble code appeared in multiple modules: the Hybrid Powertrain Control Module (HPCM), Motor Control Module 1 (MCM1), and Motor Control Module 2 (MCM2). At one point, the Power Steering Control Module (PSCM) also reported a separate code, C0895 - Control Module Voltage Below Threshold. This suggests the 48-volt system briefly dropped below its normal range.
This makes me think there could be an issue with the AC-DC inverter system, which is responsible for charging both the hybrid battery and the 12-volt system, as well as powering the hybrid AC motors. It seems possible that there was a voltage imbalance, where the 48-volt system dropped while another system experienced a spike, potentially triggering the P0563 code.
… The following is paraphrased from another post I found on the form where @j91z28d1 commented something that may be useful under "2011 Yukon Hybrid randomly shuts off with "SERVICE POWER STEERING"
Anyways, from what I understand about how the system works, when you’re regenerative charging—typically as you’re coasting to a stop—the individual hybrid battery cell voltages can rise. If any cell goes over 20.4 volts for four seconds, the system will open the main battery contactor as a safeguard. This is designed to prevent further damage to the battery, which makes sense, but it also kills the entire truck unexpectedly.
What’s tricky is that when this happens, I think there isn’t enough time for the system to trigger a check engine light. The Body Control Module (BCM) can’t activate the light on its own; it has to set a code and then send a request to the ECM over the CAN bus. By the time this process even starts, the truck has already lost power. The engine is already off, and because of the 2,000 psi accumulator, you won’t immediately notice the loss of power—especially since the hydraulic brakes continue working like normal for a while.
However, this sudden power cut is enough to trigger a low voltage code in the power steering module. The power steering system runs on the 12-volt battery but controls the 42-volt supply to the rack motor. By this logic when the main power cuts, you should see a brief “Service Power Steering System” fault pop up.
Based on my own observations and reading about the system, if you have a scanner that can read Battery control module (BCM) freeze frame data, check for a max cell voltage over 20.4 volts. If you find that, you’ve likely pinpointed the cause of the stalling and temporary power steering fault. The truck typically restarts quickly without needing to clear any codes or check engine light. A simple key cycle will reset the system, and the cell voltages will return to normal since regenerative charging is no longer active.
I drive a 2009 Hybrid Tahoe. About six months ago, I replaced the high-voltage hybrid battery, and since then (5k ish miles), I haven’t had any check engine lights or issues. Today, I drove from San Antonio to Pecos, Texas, a trip of about four hours. The car ran perfectly the entire time....
Toward the end of the trip, I knew I was cutting it close on fuel, but I had a jerry can in the trunk, so I decided to push on from Fort Stockton to Pecos. I was maintaining about 90 mph until I had to slow down to 60 mph behind a semi. I eased off the gas, letting the regenerative braking handle the slowdown.
At that point, I noticed the fuel gauge, which was close to “E” but not fully empty, suddenly dropped to empty. The fuel light came on, and the engine died. I shifted into neutral and managed to restart the engine. Knowing I was critically low on fuel, I stayed behind the semi at 60 mph for the last mile. Then, the engine died again, but I was able to coast off the highway directly to a gas station and stop at the pump.
At the pump, I filled the 24 gallon tank with 25.59 gallons and restarted the car, but it died again after about 30 seconds. Suspecting air or vapor in the fuel rail, I purged it using the Schrader valve under the hood. Initially, some fuel vapor came out, followed by steady gasoline. Thinking I’d cleared the air, I restarted the car and let it idle. It ran perfectly for five minutes.
I then drove a couple of minutes down the road, but it died again. I shifted into neutral, restarted it a few times, and managed to reach another gas station. There, I pulled over for more diagnostics.
The car showed no check engine light or trouble codes. The only issue was that it would idle for about 30 seconds before shutting off. Each time it started, it ran smoothly—no misfires, no hesitation. It would start, idle smoothly, and even rev up without issue, but it always shut down after roughly 30 seconds.
I called a mechanic in Pecos, and based on the symptoms, we both suspected a fuel system issue. When I tried starting it again, the car surprisingly ran long enough for a five-minute drive to his shop. Once there, it idled smoothly for 10-15 minutes while we examined it, but it eventually died again and displayed a “service power steering” message on the dash.
After that, we tried restarting it multiple times. It would run for about 30 seconds before shutting off each time, always running smoothly while it lasted. Using his more advanced scan tool (Snap-on), we finally pulled a trouble code: P0563 - System Voltage High.
This code hadn’t appeared on my earlier scans or triggered a check engine light. According to a GM technical bulletin for hybrid Tahoes, this code occurs when the ignition system voltage exceeds 18 volts for either six seconds or six times per second (not entirely clear which). We were able to clear the code a few times, but it kept coming back, and the car still wouldn’t idle for longer than 30 seconds.
I then had the car towed from the independent mechanic in Pecos to a Chevy/GMC dealer in Monahans. We will hopefully dive into the car tomorrow.
…
Just to provide additional context of my understanding of the General Motors two mode hybrid, the hybrid system in this vehicle operates at around 300 volts, while the air conditioner and electric power steering runs at 48 volts. All other standard car accessories, including the ignition coils, rely on the 12-14 volt system.
The DTC P0563 refers to the ignition voltage exceeding 18 volts, and I’m wondering if this could be related to the regenerative braking. When I slowed from 90 mph to 60 mph using regenerative braking, could that have caused an overcharge? After four hours of highway driving, the hybrid battery should have been fully charged.
The question is how an overvoltage could occur in the 14-volt system, which powers the ignition coils. Neither the instrument panel nor the Snap-on scanner showed anything abnormal. The dashboard consistently displayed 12-14 volts for the 12-volt system, and the Snap-on tool showed a maximum of 14.6 volts. Similarly, the hybrid high-voltage battery stayed within expected limits, peaking at 330 volts during my observations. From what I’ve read, some technicians report seeing up to 400 volts during regenerative braking, so this seems normal.
The P0563 trouble code appeared in multiple modules: the Hybrid Powertrain Control Module (HPCM), Motor Control Module 1 (MCM1), and Motor Control Module 2 (MCM2). At one point, the Power Steering Control Module (PSCM) also reported a separate code, C0895 - Control Module Voltage Below Threshold. This suggests the 48-volt system briefly dropped below its normal range.
This makes me think there could be an issue with the AC-DC inverter system, which is responsible for charging both the hybrid battery and the 12-volt system, as well as powering the hybrid AC motors. It seems possible that there was a voltage imbalance, where the 48-volt system dropped while another system experienced a spike, potentially triggering the P0563 code.
… The following is paraphrased from another post I found on the form where @j91z28d1 commented something that may be useful under "2011 Yukon Hybrid randomly shuts off with "SERVICE POWER STEERING"
Anyways, from what I understand about how the system works, when you’re regenerative charging—typically as you’re coasting to a stop—the individual hybrid battery cell voltages can rise. If any cell goes over 20.4 volts for four seconds, the system will open the main battery contactor as a safeguard. This is designed to prevent further damage to the battery, which makes sense, but it also kills the entire truck unexpectedly.
What’s tricky is that when this happens, I think there isn’t enough time for the system to trigger a check engine light. The Body Control Module (BCM) can’t activate the light on its own; it has to set a code and then send a request to the ECM over the CAN bus. By the time this process even starts, the truck has already lost power. The engine is already off, and because of the 2,000 psi accumulator, you won’t immediately notice the loss of power—especially since the hydraulic brakes continue working like normal for a while.
However, this sudden power cut is enough to trigger a low voltage code in the power steering module. The power steering system runs on the 12-volt battery but controls the 42-volt supply to the rack motor. By this logic when the main power cuts, you should see a brief “Service Power Steering System” fault pop up.
Based on my own observations and reading about the system, if you have a scanner that can read Battery control module (BCM) freeze frame data, check for a max cell voltage over 20.4 volts. If you find that, you’ve likely pinpointed the cause of the stalling and temporary power steering fault. The truck typically restarts quickly without needing to clear any codes or check engine light. A simple key cycle will reset the system, and the cell voltages will return to normal since regenerative charging is no longer active.
