GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual

Sending Units and Sensors

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REMOVAL & INSTALLATION



Engine Coolant Temperature

See Figures 1 and 2

On all vehicles covered by this manual an Engine Coolant Temperature (ECT) sensor can be found threaded into one of the engine coolant passages. The sensor is a thermistor (a resistor which changes value based on temperature) and is used on all computer controlled fuel systems to help regulate fuel and emissions systems controlled by the computer module. The sensor may be found in various places on the engine. Most engines will likely have this sensor threaded into the intake manifold, often near the thermostat housing.



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Fig. Fig. 1: On most vehicles such as the 4.3L (VIN Z) engine, the coolant temperature sensor is mounted in the intake manifold

Care must be taken when handling engine control related sensors as damage to the sensor may adversely affect engine driveability and emissions.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the engine cooling system to a level below the sensor.
  4.  
  5. Release the locktab and disengage the sensor connector.
  6.  
  7. Using a special sensor tool or a deep 12-point socket, loosen the sensor, then carefully unthread and remove it from the engine.
  8.  

To install:
  1. Thread the sensor into the engine by hand, then tighten using the socket or tool. If a replacement sensor came with instructions use a torque wrench to assure proper tightening.
  2.  

On some engines, such as the Syclone's MFI 4.3L engine, the manufacturer suggests coating the coolant sensor threads with a sealant such as 1052080, or equivalent.

  1. Engage the sensor wiring harness.
  2.  
  3. Connect the negative battery cable.
  4.  
  5. Properly refill the engine cooling system, then run the engine and check for leaks.
  6.  



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Fig. Fig. 2: Coolant temperature sensor location-4.3L (VIN W) engine

Manifold Absolute Pressure (MAP) Sensor

See Figures 3 and 4

The MAP sensor measures changes in the intake manifold pressure, resulting from changes in engine load and speed changes, then converts this to a voltage output. Other than checking for loose vacuum hoses or electrical connectors, the only service possible for this sensor is replacement, if testing shows the sensor is faulty.

  1. Disconnect the negative battery cable.
  2.  
  3. Release the locktab, then disengage the sensor electrical connector.
  4.  
  5. Either tag and disconnect the hoses from the MAP sensor or disengage the entire vacuum harness assembly from the sensor, as applicable.
  6.  
  7. Either remove the retainers or release the lock tabs, then remove the sensor from the engine.
  8.  

To install:
  1. Install the sensor and secure in position using the retainers or lock tabs, as applicable.
  2.  
  3. Connect the vacuum harness or hoses to the sensor as noted during removal.
  4.  
  5. Engage the sensor electrical connector.
  6.  
  7. Connect the negative battery cable.
  8.  



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Fig. Fig. 3: Common MAP sensor mounting (4.3L VIN Z engine shown)



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Fig. Fig. 4: MAP sensor (and other upper intake mounted component) installation-4.3L (VIN W) engine

Oxygen Sensor

Almost all vehicles covered by this manual were equipped with an oxygen sensor for feedback carburetor control . Fuel injected engines, introduced to the S/T series in 1985 and used on all of these trucks built in 1986 and later also require an oxygen sensor for computer air/fuel mixture management. On vehicles so equipped, the oxygen sensor is usually mounted in an exhaust manifold. On some engines, the sensor is mounted at the end of the crossover pipe.

  1. Disconnect the negative battery cable.
  2.  
  3. Locate the oxygen sensor. The sensor is usually mounted in the exhaust manifold or in the crossover pipe. If necessary, raise and support the front of the truck safely using jackstands.
  4.  
  5. Trace the wires leading from the oxygen sensor back to the first connector and then disengage the sensor harness connector.
  6.  

The sensor may be extremely difficult to remove when engine temperature is below 120°F (48°C). Be careful as excessive force could damage threads in the exhaust manifold or pipe.

  1. Using a special sensor tool or a socket, loosen the sensor, then carefully unthread and remove it from the engine. If sensor removal is difficult, spray a small amount of commercial heat riser solvent onto the sensor threads and allow it to soak in for at least five minutes, then attempt to loosen and remove the sensor again.
  2.  


CAUTION
Avoid using cleaning solvents of any type on the oxygen sensor. Keep the louvered end free of grease, dirt or other contaminants. Do not drop or roughly handle the sensor. If any of these cautions are ignored, the sensor could be damaged resulting in poor engine performance and excessive exhaust emissions.

To install:
  1. New oxygen sensors will be packaged with a special anti-seize lubricant already applied to the threads. If a sensor is removed from the exhaust and is to be reinstalled for any reason, the sensor threads must be coated with a fresh anti-seize compound. Use a G.M. anti-seize compound no. 5613695, no. 3613695 or an equivalent compound made of liquid graphite and glass beads. This is not a conventional anti-seize paste, the graphite will tend to burn away but the glass beads will remain. The use of a regular compound may electrically insulate the sensor, rendering it inoperative. You must coat the threads with an electrically conductive anti-seize compound.
  2.  
  3. Carefully thread the sensor into the exhaust bore, then tighten to 30 ft. lbs. (41 Nm) using a torque wrench.
  4.  
  5. Engage the sensor harness.
  6.  
  7. If raised, remove the jackstands and carefully lower the truck.
  8.  
  9. Connect the negative battery cable, then start and run the engine to check for proper operation.
  10.  

Intake Air Temperature/Manifold Air Temperature Sensor

See Figures 5, 6 and 7

Most of the fuel injected vehicles covered by this manual are equipped with either an Intake Air Temperature (IAT) or an Manifold Air Temperature (MAT) sensor. The IAT sensor is normally installed into the air ducting somewhere near or before the throttle body. If equipped with a MAT sensor, it is typically threaded into the intake manifold.

  1. Disconnect the negative battery cable.
  2.  
  3. Depress the locktab and disengage the sensor wiring.
  4.  
  5. Remove the sensor from the air duct or unthread it from the intake manifold, as applicable.
  6.  

To install:

Before installing a manifold air temperature sensor, be sure to coat the THREADS of the sensor using 1052080 or an equivalent sealant.

  1. Install and secure the sensor to the engine.
  2.  
  3. Engage the sensor wiring.
  4.  
  5. Connect the negative battery cable.
  6.  

Knock Sensor

See Figure 8

The Electronic Spark Control (ESC) knock sensor is normally mounted to the engine block or cylinder head. On these applications, the sensor can often be found on the side or end of the cylinder head. Also, on many of the se engines, the sensor is mounted in a hole which is exposes to engine coolant.

  1. Disconnect the negative battery cable.
  2.  
  3. If the sensor is located in a coolant passage, drain the engine cooling system to a level below the sensor.
  4.  

If you are not sure whether or not the sensor is threaded into a coolant passage, wait until the sensor is being loosened to determine if any coolant need to be drained. Loosen the sensor in small1/4turn increments and see if coolant begins to seep from the threads. If coolant begins to seep, retighten the sensor and drain the cooling system.

  1. Disengage the wiring harness connector from the knock sensor
  2.  
  3. Loosen and remove the sensor from the engine.
  4.  

To install:
  1. Make sure the sensor threads are clean and free of debris. If the sensor is being threaded into a coolant passage, apply a water base caulk sealant to the sensor threads. DO NOT use a silicon tape as this may insulate the sensor from the engine block.
  2.  
  3. Install the sensor to the engine and tighten to 14 ft. lbs. (19 Nm).
  4.  
  5. Engage the sensor wiring harness.
  6.  
  7. Connect the negative battery cable and check for proper engine operation.
  8.  



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Fig. Fig. 5: Common MAT sensor installation (2.5L engine shown)



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Fig. Fig. 6: Common IAT sensor and harness connector



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Fig. Fig. 7: IAT sensor location and installation-MFI and CMFI engines



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Fig. Fig. 8: Example of a knock sensor

 
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