u/QWADMASTER

Hi everyone,

I'm hoping to get some advice before I spend more money replacing parts.

I have a 2009 Chevy Cobalt LT 2.2L (automatic) with 94,000 km and the original engine.

A few weeks before it completely failed, I noticed an occasional light jerking while braking. It wasn't severe and the car otherwise drove normally.

The day it broke down, I was driving 80–90 km/h on Highway 138 with no issues. After slowing for a red light, the slight jerking happened again while braking.

When the light turned green, I accelerated and the car barely responded to the gas pedal. The engine itself wouldn't rev even with the accelerator pressed. Shortly after, the check engine light came on.

I pulled onto a side street where the car started lightly rocking/jerking back and forth. A few seconds later, the brake warning light came on, followed by the Service Traction light.

The car gradually lost power, slowed down on its own, stalled, and wouldn't restart.

After sitting for about 5–10 minutes, it started once but died after a few seconds. On the next attempt it stayed running.

While turning around in a driveway, it stalled again when I braked and shifted into reverse. I restarted it, kept it alive with a little throttle, and managed to drive it home.

On the drive home it wouldn't accelerate properly. It would barely go over 20 km/h at first, eventually reached about 50 km/h, but would not go any faster. Every time I slowed down or came to a complete stop, it would jerk again and try to stall.

Now the car only cranks. It sounds like it wants to start and occasionally tries to fire, but never fully starts. I also think I can smell fuel after cranking.

The only code stored is **P0641 (5V Reference Circuit)**.

So far I've replaced:

- MAP sensor

- Crankshaft position sensor

Neither fixed the problem.

I haven't checked for spark, fuel pressure, or the 5V reference voltage yet. I only have a basic code reader.

Has anyone dealt with this exact issue on a Cobalt or another GM vehicle? Based on the symptoms, does this sound more like a wiring harness issue, a sensor shorting the 5V reference, a bad PCM, or something else?

If this were in your shop, what would be the very first things you'd test before replacing any more parts?

Any advice is greatly appreciated. Thanks!

Hi everyone,

I'm hoping to get some advice before I spend more money replacing parts.

I have a 2009 Chevy Cobalt LT 2.2L (automatic) with 94,000 km and the original engine.

A few weeks before it completely failed, I noticed an occasional light jerking while braking. It wasn't severe and the car otherwise drove normally.

The day it broke down, I was driving 80–90 km/h on Highway 138 with no issues. After slowing for a red light, the slight jerking happened again while braking.

When the light turned green, I accelerated and the car barely responded to the gas pedal. The engine itself wouldn't rev even with the accelerator pressed. Shortly after, the check engine light came on.

I pulled onto a side street where the car started lightly rocking/jerking back and forth. A few seconds later, the brake warning light came on, followed by the Service Traction light.

The car gradually lost power, slowed down on its own, stalled, and wouldn't restart.

After sitting for about 5–10 minutes, it started once but died after a few seconds. On the next attempt it stayed running.

While turning around in a driveway, it stalled again when I braked and shifted into reverse. I restarted it, kept it alive with a little throttle, and managed to drive it home.

On the drive home it wouldn't accelerate properly. It would barely go over 20 km/h at first, eventually reached about 50 km/h, but would not go any faster. Every time I slowed down or came to a complete stop, it would jerk again and try to stall.

Now the car only cranks. It sounds like it wants to start and occasionally tries to fire, but never fully starts. I also think I can smell fuel after cranking.

The only code stored is **P0641 (5V Reference Circuit)**.

So far I've replaced:

- MAP sensor

- Crankshaft position sensor

Neither fixed the problem.

I haven't checked for spark, fuel pressure, or the 5V reference voltage yet. I only have a basic code reader.

Has anyone dealt with this exact issue on a Cobalt or another GM vehicle? Based on the symptoms, does this sound more like a wiring harness issue, a sensor shorting the 5V reference, a bad PCM, or something else?

If this were in your shop, what would be the very first things you'd test before replacing any more parts?

Any advice is greatly appreciated. Thanks!

Hi everyone,

I'm hoping to get some advice before I spend more money replacing parts.

I have a 2009 Chevy Cobalt LT 2.2L (automatic) with 94,000 km and the original engine.

A few weeks before it completely failed, I noticed an occasional light jerking while braking. It wasn't severe and the car otherwise drove normally.

The day it broke down, I was driving 80–90 km/h on Highway 138 with no issues. After slowing for a red light, the slight jerking happened again while braking.

When the light turned green, I accelerated and the car barely responded to the gas pedal. The engine itself wouldn't rev even with the accelerator pressed. Shortly after, the check engine light came on.

I pulled onto a side street where the car started lightly rocking/jerking back and forth. A few seconds later, the brake warning light came on, followed by the Service Traction light.

The car gradually lost power, slowed down on its own, stalled, and wouldn't restart.

After sitting for about 5–10 minutes, it started once but died after a few seconds. On the next attempt it stayed running.

While turning around in a driveway, it stalled again when I braked and shifted into reverse. I restarted it, kept it alive with a little throttle, and managed to drive it home.

On the drive home it wouldn't accelerate properly. It would barely go over 20 km/h at first, eventually reached about 50 km/h, but would not go any faster. Every time I slowed down or came to a complete stop, it would jerk again and try to stall.

Now the car only cranks. It sounds like it wants to start and occasionally tries to fire, but never fully starts. I also think I can smell fuel after cranking.

The only code stored is **P0641 (5V Reference Circuit)**.

So far I've replaced:

- MAP sensor

- Crankshaft position sensor

Neither fixed the problem.

I haven't checked for spark, fuel pressure, or the 5V reference voltage yet. I only have a basic code reader.

Has anyone dealt with this exact issue on a Cobalt or another GM vehicle? Based on the symptoms, does this sound more like a wiring harness issue, a sensor shorting the 5V reference, a bad PCM, or something else?

If this were in your shop, what would be the very first things you'd test before replacing any more parts?

Any advice is greatly appreciated. Thanks!