Active Fuel Management

[crothmeier]

Car: 2007 Chevrolet Impala LTZ

Miles: 131,300

Does anyone have a GM vehicle with an active fuel management vehicle engine? I recently had the check engine light come on shortly after noticing my Impala quit dropping down to 3 cylinders while coasting. I took it in to the local dealer, had the codes read, and it came back as a faulty oil pressure sending unit. I had a new one installed yesterday, the light went off, and the problem with the not dropping down to 3 cylinders is still there.

When I start coasting, it lets off the gas, then gets on it, and off, and on. its really noticeable even to passengers, described as a herky-jerky feeling. I read on a GM forum the list of things that can inhibit the active fuel management from working properly. One thing was "engine oil pressure out of range" in amongst about 20 other reasons.

It doesn't throw a code, nothing shows up when its read, and the dealership tells me they haven't seen anything like it before. I'm just fishing to see if anyone else has experienced this. I'm more than likely going to take it in and start the expensive procedure of troubleshooting.

Below is the list of things that can inhibit that I found from GM:

Cylinder Deactivation Inhibit Reasons

Listed below are the powertrain conditions that will inhibit V4 mode, while operating under light load driving conditions:

• Engine manifold vacuum low

• Brake booster vacuum pressure low

• Accelerator pedal position rate of increase too high, electronic throttle control

• Accelerator pedal position too high, electronic throttle control

• Ignition voltage out of range

• Engine oil pressure out of range

• Engine oil temperature out of range

• Engine RPM out of range

• Transmission gear incorrect

• Transmission range incorrect

• Transmission gear shift in progress

• All cylinders activated via scan tool output control

• Minimum time in V8 mode not met

• Maximum V4 mode time exceeded

• Engine oil aeration present

• Decel fuel cutoff active

• Fuel shut-off timer active

• Minimum heater temp low, HVAC system

• Reduced engine power active, electronic throttle control

• Brake torque management active

• Axle torque limiting active

• Engine metal over temperature protection active

• Catalytic converter over temperature protection active

• Piston protection active, knock detected

• Hot coolant mode active

• Engine over speed protection active

• Fault Active or Fault Pending--cylinder deactivation is disabled for the following faults:

- Brake Booster Vacuum Sensor

- Manifold Absolute Pressure Sensor

- Engine Oil Pressure Sensor

- Engine Coolant Temperature Sensor

- Vehicle Speed Sensor

- Crankshaft Position Sensor

- Engine Misfire Detected

- Cylinder Deactivation Solenoid Driver Circuit