GM 96056758 Sensor, Water Temperature

Most components in 1989 through 1991 Geo Metro models have an extended warranty coverage from the government which makes it difficult to perform component checks or replacements during the warranty period. Both sensors found in electrical position determine exhaust gas oxygen levels within the exhaust manifold and catalytic converter which detects emission levels respectively where circuit failures produce code 13. A failure within the TBI unit coolant temperature sensor thermistor will trigger a code 14 or 15 while a check requires resistance tests with an ohmmeter and replacement with Teflon tape or thread sealant to stop leaks. A failure in the manifold air temperature (MAT) sensor located in the air cleaner housing produces a code 24 which should be diagnosed by a dealer. A faulty manifold absolute pressure sensor cannot be repaired thus it requires complete unit replacement because it transforms the manifold pressure fluctuations into an electronic signal for fuel control through ECM. Manual transaxle cars use a throttle switch (TS) to check throttle valve angle whereas automatic transaxle vehicles utilize a throttle position sensor (TPS) to accomplish the same function. Both devices trigger error codes 21 or 22 that demand professional diagnostics for proper fix. A failure of the vehicle speed sensor (VSS) which is integrated with the speedometer causes a pulsing voltage signal to the ECM for speed calculation and produces error code 24. This diagnosis requires professional attention from a dealer. Engine speed calculation and device control operations derive from the crank angle sensor which exists as a component of the distributor to produce alternating voltage pulses.

The coolant temperature indicator system features a temperature gauge in the instrument panel and a coolant temperature sending unit on the cylinder head, with variations in location depending on the model type; carbureted models have the sending unit below the thermostat housing, while pre-OBD-II models place it on the intake manifold, and later models also use the intake manifold. Some vehicles may have multiple sending units, but only one is utilized for the gauge, while others serve as sensors for the air conditioning system or the Transmission Control Module (TCM). Fuel-injected vehicles include an Engine Coolant Temperature (ECT) sensor that monitors coolant temperature for the Powertrain Control Module (PCM), located in different positions based on engine type. To distinguish between a temperature sending unit and an ECT sensor, count the wires: sending units have one wire, while ECT sensors have two or three. In 1996 and later models, the ECT sensor acts as both the sending unit for the gauge and the information sensor for the PCM. In case of overheating, check the coolant level and ensure the wiring between the gauge and switch is secure, along with intact fuses. To test the circuit, ground the wire to the switch with the ignition on (engine off for safety); if the gauge deflects fully, the sending unit needs replacement. To replace the sending unit, unscrew it from the engine, apply sealant to the threads, and ensure the engine is cool before removal, as coolant will be lost during the process, so be ready to catch it and check the level after installation.

It should be prepared by applying a Teflon tape or light coat of sealant to the threads.

The ECT sensor is located on the back of the engine on DOHC engines.

Diagnostic trouble codes are set if there is a malfunction in the ATS or IAT sensor circuit.