Stop Start System Diagnosis

WARNING: This page is about a different car, the 2018 Jeep Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

For diagnostics of the starting system, please. Refer to DIAGNOSIS AND TESTING .

For diagnostics of the Stop Start system, the scan tool can be used to review the inhibitor menu to help root cause a potential Stop Start concern.

Possible Reasons The Engine Does Not AUTO STOP

Prior to engine shut down, the system will check many safety and comfort conditions to see if they are fulfilled. In following situations the engine will not stop:

Driver's seat belt is not buckled.
Battery or outside temperature is less than -15°C (5°F) or greater than 60°C (140°F).
Actual cabin temperature is significantly different than temperature set on Auto HVAC.
HVAC is set to full defrost mode.
Engine has not reached normal operating temperature.
Battery discharged.
When driving in REVERSE.
Hood is open. for further information on the Hood Ajar Switch operation and diagnostics. Refer to SWITCH, HOOD AJAR, DESCRIPTION .
Vehicle is in 4LO transfer case mode.

It may be possible for the vehicle to be driven several times without the STOP/START system going into a STOP/START READY state under more extreme conditions of the items listed above.

For a more technical and detailed explanation of AutoStop, review the following inhibitors.

When it comes to Stop Start, we allow AutoStop event if:

Accelerator pedal is in the rest position.
HVAC Control allows an auto stop event. The AC load can not be in a high demand mode of operation.
Battery state (charge 65%, function 8 volts, health 40 ampere hour) is within an acceptable range.
Current master cylinder brake pressure exceeds the required Hill Speed Assist (HSA) brake pressure and is sufficient to hold the vehicle on a grade.
Electronic Stability Control (ECS) is not requesting control.
Fuel level is greater than the minimum fuel level threshold.
Both hood switches indicate the hood is closed.
Predefined OBD faults are not present.
Vehicle occupants are not attempting a vehicle exit maneuver.
Absolute Barometric Pressure is within range. Barometric pressure is greater then a minimum of 605KPa.
Brake Booster is sufficient to maintain master cylinder pressure with current applied pedal force. Minimum 205Ka.
Starter motor engagement has not exceeded prescribed frequency use.
Vehicle speed is 0.
Steering angle has not exceeded the prescribed range.
Steering torque is less than the prescribed value.
Ambient Air Temperature is within the prescribed range (-17F - 40F).
Catalyst temperature is within the prescribed range (150F - 950F).
Coolant temperature is within the prescribed range.
Engine oil temperature is within the prescribed range (40C - 110C).
Anti-lock brake system is not active.
Transfer case is not in 4WDLO.
Vehicle is not in tow haul mode.
Vehicle is in valid target gear and brake switch combination.
Threshold vehicle speed exceeded or timeout since last shift out of reverse.
Transmission ready.
Battery temperature is within the prescribed range (-256F - 256F).
Engine speed is below a set threshold of 1000 RPM.
Engine runtime is greater then threshold of 3 seconds.
Start Stop disable switch is not active.
Flex fuel learn mode is not active.
Vehicle is not on a grade.
Threshold vehicle speed exceeded since last engine start is 8 mph.

Conditions that will cause the engine to start automatically while in STOP/START AUTO STOP ACTIVE mode:

Actual cabin temperature is significantly different than temperature set in Auto HVAC.
HVAC is set to full defrost mode.
STOP/START AUTO STOP TIME ACTIVE exceeds 5 minutes.
Battery Voltage drops too low.
Low brake vacuum e.g. after several brake pedal applications.
Vehicle is moving faster then 3 mph (5 km/h).
STOP/START OFF switch is pressed.
4WD is put into 4LO mode.

We allow Stop Start AutoStarts to occur when any of the conditions are made active:

Accelerator pedal is in the "rest" position.
HVAC Control is allows an Auto Stop event.
Battery State (charge, function, health) is within acceptable range.
Current master cylinder brake pressure exceeds the required HSA brake pressure and is sufficient to hold the vehicle on a grade.
Electronic Stability Control system is not requesting control.
Fuel Level is greater than the minimum fuel level threshold.
Both hood switches indicate hood is closed.
Predefined OBD faults are not present.
Vehicle occupants are not attempting a vehicle exit maneuver.
Absolute Barometric Pressure is within range.
Brake Booster Pressure is sufficient to maintain master cylinder pressure with current applied pedal force.
Starter motor engagement has not exceeded prescribed frequency of use.
Vehicle speed is 0.
Steering Angle has not exceeded the prescribed range.
Steering Torque is less than the prescribed value.
Ambient Air Temperature is within the prescribed range.
Catalyst Temperature is within the prescribed range.
Coolant Temperature is within the prescribed range.
Engine Oil Temperature is within the prescribed range.
Anti-Lock Brake System is not active.
Transfer Case Mode is not in 4WDLO.
Vehicle is not in TOW-HAUL mode.
Vehicle is in valid target gear and brake switch state combination.
Threshold vehicle speed exceeded or timeout since last shift out of reverse.
Transmission ready.
Battery temperature is within the prescribed range.
Engine speed is below a set threshold.
Threshold vehicle speed exceeded since last engine start.
Engine runtime greater than threshold.
Stop-Start disable switch is not active.
Flex fuel learn mode not active.
Vehicle is not on a grade.

We allow Stop Start AutoStarts to occur when any of the conditions are made active:

Accelerator pedal is not in the "rest" position.
HVAC Control is active.
Battery State (charge, function, health) is out of range.
Current master cylinder brake pressure does not have enough HSA brake pressure.
Electronic Stability Control system is requesting control.
Fuel Level is lower than the minimum fuel level threshold.
One or both hood switches indicate hood is open.
Predefined OBD faults are present.
Absolute Barometric Pressure is out of range.
Brake Booster Pressure is insufficient to maintain master cylinder pressure with current applied pedal force.
Starter motor engagement has exceeded prescribed frequency of use.
Vehicle speed is above 0.
Steering Angle has exceeded the prescribed range.
Steering Torque is more than the prescribed value.
Ambient Air Temperature is outside the prescribed range.
Catalyst Temperature is outside the prescribed range.
Coolant Temperature is outside the prescribed range.
Engine Oil Temperature is outside the prescribed range.
Anti-Lock Brake System is active.
Transfer Case Mode is in 4WDLO.
Vehicle is in TOW-HAUL mode.
Transmission not ready.
Battery temperature is out of the prescribed range.
Stop-Start disable switch is active.
Flex fuel learn mode is active.

The above conditions can restart the vehicle as long as:

Completed initial engine key start.
Occupant sensing allow engine start condition met.
OBD allow engine start condition met.
Vehicle hood closed.

System Malfunction:

If there is a malfunction in the STOP/START system, the system will not shut down the engine. A SERVICE STOP/START SYSTEM message will appear in the EVIC.