8524 690 01 Rev. K KohlerEngines.com
EFI SYSTEM-BOSCH
Code 31
Component: Fuel Mixture or Oxygen Sensor
Fault: System too lean. Oxygen sensor not
sending expected voltage to ECU.
Condition: System operates under “open loop”
control only. Until fault is detected and
registered by ECU, engine will run rich
if oxygen sensor is shorted to ground
or lean if it is shorted to battery voltage.
After fault is detected, performance can
vary, depending on cause. If performance
is pretty good, problem is probably with
the oxygen sensor, wiring, or connectors.
If engine is still running rich (laboring,
short on power) or lean (popping or
misfi ring), fuel mixture is suspect,
probably incorrect TPS initialization or
low fuel pressure.
Conclusion: TPS Initialization Incorrect
● Lean condition (check oxygen sensor
signal with VOA and see Oxygen
Sensor section).
Engine Wiring Harness Related
● Pin circuit wiring or connectors.
Pin 10 for “35 Pin” (MA 1.7) Metal-
Cased ECU.
Pin 11 for “24 Pin” (MSE 1.0)
Plastic-Cased ECU.
Pin 20 for “32 Pin” (MSE 1.1)
Plastic-Cased ECU.
Low Fuel Pressure
Oxygen Sensor Related
● Sensor connector or wiring problem.
● Exhaust leak.
● Poor ground path to engine (sensor is
case grounded).
Poor system ground from ECU to engine,
causing rich running while indicating lean.
Code 32
Component: Oxygen Sensor
Fault: No change in sensor output signal.
Condition: Open loop operation only, may cause
a drop in system performance and fuel
effi ciency.
Conclusion: Engine Wiring Harness Related
● Pin circuit wiring or connectors.
Pin 10 for “35 Pin” (MA 1.7)
Metal-Cased ECU.
Pin 11 for “24 Pin” (MSE 1.0)
Plastic-Cased ECU.
Pin 20 for “32 Pin” (MSE 1.1)
Plastic-Cased ECU.
Oxygen Sensor Related
● Sensor connector or wiring problem.
● Sensor contaminated or damaged.
● Sensor below minimum operating
temperature (375°C, 709°F).
● Poor ground path from sensor to
engine (sensor grounds through shell,
see Oxygen Sensor section).
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