Volvo

The Ambient Pressure Sensor is located inside the Engine Control Module (ECM) and can therefore not be checked.
The signal is used to calculate intake manifold pressure (IMP) as well as to compensate for fuel when driving at high altitudes.
The engine control module (ECM) will set a diagnostic trouble code (DTC) if the sensor signal is not within predetermined limits, or the signal is not rational.

Conditions for diagnostic trouble code (DTC):
1) The barometric pressure (BARO) from the sensor is irrational

Observable symptoms
1) Poor response at high altitudes

Probable cause
1) Barometric Pressure (BARO) Sensor

Detailed information
1) The sensor is located in the engine control module (ECM) and therefore cannot be checked
2) The signal is used to calculate intake manifold pressure (IMP) as well as to control fuel compensation when driving at high altitudes
3) If the sensor is blocked by e.g. dirt, paint or stickers it may send an incorrect value

The Engine Coolant Temperature Sensor is a thermistor. The resistance of the Engine Coolant Temperature Sensor changes inversely to the temperature of the engine coolant. When the coolant is cold, the sensor resistance is high. As the temperature of the coolant increases, the sensor resistance decreases.
The Engine Control Module (ECM) monitors the voltage drop across the Engine Coolant Temperature Sensor.
The coolant temperature signal is used to calculate fuel injection and to evaluate operating conditions of the engine coolant temperature. Examples of conditions that may cause high coolant temperature are: thermostat failure, fan failure, heavy load, high ambient temperatures and radiator blockage.
The sensor’s signal is monitored by the Engine Control Module (ECM).
The engine control module (ECM) will set a diagnostic trouble code (DTC) and derate the engine to avoid engine damage if the sensor signal is not within predetermined limits, or the signal is not rational.

Conditions for diagnostic trouble code (DTC):
1) The sensor signal is stuck
2) Sensor value does not change with changing conditions
3) Extreme variation in sensor values

Probable cause
1) Air in the coolant
2) Wiring harness
3) Connector
4) Engine coolant temperature sensor
5) Thermostat

The Engine Coolant Temperature Sensor is a thermistor. The resistance of the Engine Coolant Temperature Sensor changes inversely to the temperature of the engine coolant. When the coolant is cold, the sensor resistance is high. As the temperature of the coolant increases, the sensor resistance decreases.
The Engine Control Module (ECM) monitors the voltage drop across the Engine Coolant Temperature Sensor.
The coolant temperature signal is used to calculate fuel injection and to evaluate operating conditions of the engine coolant temperature. Examples of conditions that may cause high coolant temperature are: thermostat failure, fan failure, heavy load, high ambient temperatures and radiator blockage.
The sensor’s signal is monitored by the Engine Control Module (ECM).
The engine control module (ECM) will set a diagnostic trouble code (DTC) and derate the engine to avoid engine damage if the sensor signal is not within predetermined limits, or the signal is not rational.

Conditions for diagnostic trouble code (DTC):
1) Temperature too high

Observable symptoms
1) A buzzer sounds
2) Engine de-rated

Probable cause
1) Engine cooling fan
2) Fan belt
3) Thermostat
4) Low coolant level
5) Clogged radiator
6) Clogged cooling system
7) Coolant pump drive belt
8) Coolant pump belt tensioner
9) Slipping impeller
10) Poor flow-through in the cooling system
11) Pressure cap, expansion tank
12) Engine coolant temperature sensor
13) Engine control module (ECM)

Conditions for diagnostic trouble code (DTC):
1) The engine coolant temperature (ECT) is above 111??C (232??F)

Observable symptoms
1) High derate with potentional engine shutdown
2) Probable cause
3) Extreme driving conditions
4) Coolant thermostat
5) Engine cooling fan
6) Radiator
7) Engine Cooling System
8) Coolant pump
9) Cylinder Head
10) Oil cooler

The Engine Coolant Temperature Sensor is a thermistor. The resistance of the Engine Coolant Temperature Sensor changes inversely to the temperature of the engine coolant. When the coolant is cold, the sensor resistance is high. As the temperature of the coolant increases, the sensor resistance decreases.
The Engine Control Module (ECM) monitors the voltage drop across the Engine Coolant Temperature Sensor.
The coolant temperature signal is used to calculate fuel injection and to evaluate operating conditions of the engine coolant temperature. Examples of conditions that may cause high coolant temperature are: thermostat failure, fan failure, heavy load, high ambient temperatures and radiator blockage.
The sensor’s signal is monitored by the Engine Control Module (ECM).
The engine control module (ECM) will set a diagnostic trouble code (DTC) and derate the engine to avoid engine damage if the sensor signal is not within predetermined limits, or the signal is not rational.

Observable symptoms
1) High fuel consumption
2) The engine coolant temperature (ECT) gauge shows 0
3) Engine fan constantly engaged

Probable cause
1) Engine coolant temperature sensor
2) Connector
3) Wiring harness
4) Engine control module (ECM)

The Engine Coolant Temperature Sensor is a thermistor. The resistance of the Engine Coolant Temperature Sensor changes inversely to the temperature of the engine coolant. When the coolant is cold, the sensor resistance is high. As the temperature of the coolant increases, the sensor resistance decreases.
The Engine Control Module (ECM) monitors the voltage drop across the Engine Coolant Temperature Sensor.
The coolant temperature signal is used to calculate fuel injection and to evaluate operating conditions of the engine coolant temperature. Examples of conditions that may cause high coolant temperature are: thermostat failure, fan failure, heavy load, high ambient temperatures and radiator blockage.
The sensor’s signal is monitored by the Engine Control Module (ECM).
The engine control module (ECM) will set a diagnostic trouble code (DTC) and derate the engine to avoid engine damage if the sensor signal is not within predetermined limits, or the signal is not rational.

Conditions for diagnostic trouble code (DTC):
1) The sensor signal is stuck
2) Sensor value does not change with changing conditions
3) Extreme variation in sensor values

Probable cause
1) Air in the coolant
2) Wiring harness
3) Connector
4) Engine coolant temperature sensor
5) Thermostat

Conditions for diagnostic trouble code (DTC):
1) The voltage at pin A14.EB:27 is less than 0.17?V

Diagnostic operating conditions
1) Ignition key in ON position

Observable symptoms
1) High fuel consumption
2) The engine coolant temperature (ECT) gauge shows 0
3) Engine fan constantly engaged
4) Less powerful engine since the fan takes power from the engine

Probable cause
1) Connector
2) Wiring harness
3) Engine coolant temperature sensor
4) Engine Control Module

Conditions for diagnostic trouble code (DTC):
1) The voltage at pin A14.EB:27 is more than 4.92?V

Diagnostic operating conditions
1) Ignition key in ON position

Observable symptoms
1) High fuel consumption
2) The engine coolant temperature (ECT) gauge shows 0
3) Engine fan constantly engaged

Probable cause
1) Connector
2) Wiring harness
3) Engine coolant temperature sensor
4) Engine Control Module

Voltage from the engine control module (ECM) is applied to the engine coolant level (ECL) switch when the ignition switch is in the ON position. When the reservoir runs low, the float will be lowered on the coolant level sensor. The signal to the ECM will indicate low coolant.
If the engine control module (ECM) detects that the coolant level switch has experienced a power loss or that the level can not be detected, the ECM will set a diagnostic trouble code (DTC) and derate the engine to avoid engine damage.

Conditions for diagnostic trouble code (DTC):
1) Coolant Critically low level

Observable symptoms
1) Power loss
2) High derate with potentional engine shutdown

Probable cause
1) Low coolant level
2) The sensor float is stuck
3) Connector
4) Wiring harness
5) Engine Coolant Level (ECL) Sensor
6) Engine control module (ECM)