Auxiliary Transmission Fluid Pump (Stop Start Applications)

For Stop Start applications, an Electronic Auxiliary Transmission Oil Pump (ePump) has been added to the transmission to allow clutches to stay engaged when the engine stops. The auxiliary pump is an electric external pump bolted to the transmission case. This allows quicker response on restarts since the transmission is ready before the main pump begins outputting pressure.

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The Electronic Auxiliary Transmission Oil Pump is a "smart" device - the PCM or TCM communicates with the pump via 2 Pulse Width Modulated (PWM) hardwires:

• PCM or TCM outputs a commanded pump speed to the pump using a PWM signal:

  Duty Cycle	RPM of Motor
  0 - 9.9%	Reserved for diagnostics
  10 - 19.9%	Off state
  20 - 22.9%	100 rpm (pre-shipment supplier test)
  23 - 90%	937.14 rpm to 4, 000 rpm (linear range of operation)
  90.1 - 100%	Reserved for diagnostics

• The pump outputs the fault status of the pump to the PCM or TCM using a PWM signal. The fault status is used to stores the appropriate DTC in the PCM or TCM.

  Duty Cycle	Indicated Operating Condition	DTC	Definition
  0-10%	Out of Range low	P0C2D	Electric Transmission Fluid Pump Control Module Feedback Signal Low
  10-15%	Under Current, Correct Speed	P0C27	Electric/Auxiliary Transmission Fluid Pump "A" Motor Current Low
  20-25%	Over Current, Correct Speed	P0C28	Electric/Auxiliary Transmission Fluid Pump "A" Motor Current High
  30-34%	Over Temperature	P175A	Transmission Fluid Over Temperature Condition - Electric Transmission Fluid Pump Disabled
  35-40%	Stalled	P0C2A	Electric/Auxiliary Transmission Fluid Pump "A" Motor Stalled
  45-50%	Correct Current and Speed	n/a
  55-60%	Over Speed, Correct Current	P0B0D	Electric/Auxiliary Transmission Fluid Pump Motor Control Module
  65-70%	Under Speed, Correct Current	P0B0D	Electric/Auxiliary Transmission Fluid Pump Motor Control Module
  75-80%	Current and Speed out of Range	P0C29	Electric/Auxiliary Transmission Fluid Pump "A" Driver Circuit Performance
  85-90%	No Command Signal Received from PCM	P2796	Electric Transmission Fluid Pump Control Circuit
  90-100%	Out of range high	P0C2E	Electric Transmission Fluid Pump Control Module Feedback Signal High
  Frequency out of range or duty cycle between valid ranges	Signal should be 120 Hz +/- 20 Hz. Should not see in-range but unused duty cycle values	P0C2C	Electric Transmission Fluid Pump Control Module Feedback Signal Range/Performance

Failures of the pump take the Stop Start system out of operation - if stopped the engine will restart, then will no longer stop for the remainder of the current drive cycle.