0385843 JOHNSON CARBURETOR ASSY.

Illustration 1 g00857118
Top and right side view
(1) Coolant temperature sensor
(2) Optional coolant level sensor
Illustration 2 g00857069
Left side view
(3) Optional fuel temperature sensor
(4) Injection actuation pressure sensor
(5) Boost pressure sensor
(6) Inlet air temperature sensor
(7) Oil temperature sensor
(8) Optional fuel pressure sensor
(9) Customer connector
(10) Engine speed/timing sensors
(11) Service tool connector
(12) Oil pressure sensor Illustration 1 and Illustration 2 show the typical locations of the sensors for a 3126B Marine Engine. Specific engines may appear different from the illustration.Failure of Sensors
All Sensors
A failure of any of the sensors may be caused by one of the following malfunctions:
Sensor output is open.
Sensor output is shorted to "- battery" or "+ battery".
Measured reading of the sensor is out of specification.Coolant Temperature Sensor
Coolant temperature sensor (2) monitors engine coolant temperature. This feature is used for the engine system diagnostics with an output from the ECM. The output of the ECM can indicate a high coolant temperature through a relay or a lamp.Failure of the Coolant Temperature Sensor
The ECM will detect a failure of the coolant temperature sensor. The diagnostic lamp will warn the operator about the status of the coolant temperature sensor. Strategies that are related to the coolant temperature sensor will be disabled if a failure occurs. A failure of the coolant temperature sensor will not cause a shutdown of the engine or any horsepower change.Engine Speed/Timing Sensors
If the ECM does not receive a signal from the primary speed/timing sensor, the "DIAGNOSTIC" lamp will indicate a diagnostic fault code which will be logged in the ECM memory. If the ECM does not receive a signal from the primary speed/timing sensor, the ECM will read the signal from the secondary speed/timing sensor. The ECM continually checks in order to determine if there is a signal from both sensors (9). If either sensor fails, the faulty sensor should be replaced.Intermittent failure of the sensors will cause erratic engine control.Inlet Air Temperature Sensor
Inlet air temperature sensor (6) measures the temperature of the inlet air. The Electronic Control Module (ECM) monitors the signal of the inlet air temperature sensor. The output of the ECM can indicate high inlet air temperature through a relay or a lamp. The inlet air temperature sensor will not cause a shutdown of the engine or any horsepower change.Boost Pressure Sensor
Boost pressure sensor (5) provides a signal which corresponds to boost to the ECM. The air/fuel ratio control utilizes the actual engine speed and the boost pressure sensor in order to control the transient smoke level. The ECM can control injection timing and the amount of fuel that is injected. When the throttle is increased and when the engine demands more fuel, the fuel limit is controlled in order to reduce overall smoke levels of the engine exhaust.Failure of the Boost Pressure Sensor
The ECM will detect failure of the boost pressure sensor. The operator will be warned of the problem through the diagnostic lamp. The strategies that are related to the boost will be disabled. Engine power will be severely reduced in the event of a failure of the boost pressure sensor. A failure of the boost pressure sensor will not cause a shutdown of the engine.