GM Stop/Start System Saves Fuel, Reduces Emissions

The Stop/Start system (RPO KL9) is currently available on many newer GM vehicles, including 2014–2018 Chevrolet Malibus, 2016–2018 Buick Encores, 2017–2018 GMC Acadias and a host of Cadillac models, such as the 2016–2018 CT6 and the 2017–2018 XT5 and CTS.
When the brake pedal is pressed and the vehicle comes to a full stop, the Stop/Start system automatically turns off the vehicle’s engine (referred to as an Auto Stop). Upon releasing the pedal or pressing the accelerator, the engine restarts. About three seconds pass from release of the brake pedal to the start of the engine.
All GM Stop/Start systems operate fundamentally in the same way. The Engine Control Module (ECM) monitors various inputs, such as engine coolant temperature, vehicle speed and brake and accelerator pedal position to determine when the engine should be turned off.
These systems also use an enhanced starter to better manage the increased number of engine starts. It features a high-performance electric motor and a pinion engagement mechanism that’s stronger than conventional starters. It can also exercise independent control of the pinion and the motor.

The Two-Battery Stop/Start system uses a pair of 12V AGM batteries
  • Dual Battery Isolation Module
  • 12 Volt Absorbent Glass Mat (AGM) Primary Button
  • Auxiliary 12 Volt AGM Battery

GM vehicles have utilized three types of 12V Stop/Start systems:
  1. a Two-Battery system
  2. a DC-to-DC version with a power supply transformer
  3. an Ultra Capacitor design that provides a voltage boost during engine restarts 

The Two-Battery system relies on a primary and an auxiliary 12V Absorbent Glass Mat (AGM) battery. AGM batteries, incidentally, are used in all GM models with Stop/Start technology and they’re available through ACDelco. The vehicle’s Dual Battery Control Module is designed to switch between the primary and auxiliary battery to support vehicle loads and battery charging.
In a DC-to-DC system, a power supply transformer helps power vehicle loads temporarily when the engine cranks. It also monitors battery voltage and provides a boost of voltage to the radio, instrument cluster and other components when the engine restarts.

In a DC-DC system, a transformer helps power vehicle loads while the engine cranks.

Some vehicles with this system include an ECO (Economy) switch that allows the driver to change the air conditioning mode to Off, Comfort or Economy, which alters the parameters for activation of the Stop/Start system. In Comfort mode, for example, the focus is on passenger comfort, while the Economy setting enhances fuel efficiency.
On Cadillac models with the DC-DC system, the Stop/ Start feature can be disabled via a button on the instrument panel.
Along with initiating engine restarts, the Ultra Capacitor Stop/Start system is designed to deliver additional power to the vehicle’s electrical system. The high voltage drop caused by current drawn during a restart is compensated by voltage supplied through a pair of double-layer capacitors that store energy in an electric field. While the Stop/Start system is automatically enabled at every ignition cycle, drivers can deactivate it through a switch on the instrument panel or center console.


When the engine shuts off, the tachometer needle rests on Auto Stop.

Aside from applying the brake pedal and coming to a complete stop, certain conditions must exist for an Auto Stop event to occur, including:
  • Initial minimum vehicle speed during the drive cycle must reach at least 20 km/h 
  • With a manual transmission, the vehicle must be in Neutral and the clutch pedal fully released
  • Vehicle speed is less than 5 km/h, and engine rpm is below 1500
  • Battery voltage is greater than 12V
The following conditions will enable an engine restart:
  • The transmission shift lever is moved from the Drive position
  • With a manual transmission, the clutch pedal is depressed
  • Battery voltage is less than 11V
  • Auto Stop time exceeds two minutes.

Technical Questions? Contact an ACDelco Technical Assistance Centre agent at 1-800-263-3526 prompt 2.*

*Flat rate charge per case. Rates based on active program membership at the time of the call.