Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSVOLVO1991240 L4-2.3L SOHC VIN 88 B230FREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSCOOLANT TEMPERATURE SENSOR/SWITCH (FOR COMPUTER)TESTING AND INSPECTIONIGNITION
1991 Volvo 240 L4-2.3L SOHC VIN 88 B230F
Ignition
1991 Volvo 240 L4-2.3L SOHC VIN 88 B230FSECTION Ignition
TESTING PROCEDURE:
NOTE: While trouble shooting, always check the wiring, fuses and connectors for good condition and routing. Use the wiring diagrams found in ELECTRICAL DIAGRAMS to supplement your testing efforts.
1. Turn ignition OFF.
2. Access ignition ECU by removing the passenger side kick panel and glove compartment.
3. Remove ECU connector by pushing out the catch and folding out the wire cluster.
4. Check ignition ECU ground connections at intake manifold. They should make good contact.
5. Remove connector protective sleeve.
IMPORTANT:
Never check connections from the front. Connectors can get damaged and worsen the problem.
Check connections through the holes in the connector.
Connection pin numbers are printed on the connector side.
6. Check that terminal contacts have been pushed down evenly in connector.
7. If any connectors have been pushed down to far, poor connection may result.
8. Check main power supply by connecting a voltmeter between pin 5 (red) in ECU connector and ground.
Reading: approx. 12 volts
9. If no voltage registers, check wire between ECU and in-line fuse on left suspension strut tower. Check fuse and wiring to battery (incl. battery terminals). Repair as necessary.
10. To check the coolant temperature sensor, connect an ohm meter between ECU connector pin 2 (blue-red) and ground.
11. Resistance depending on coolant temperature should be (also see chart):
-10°C (14°F) 8,260 - 10,560 ohms
+20°C (68°F) 2,280 - 2,720 ohms
+80°C (176°F) 290 - 364 ohms
12. If a fault occurs, measure at coolant temperature sensor to see if the sensor or the wiring is the problem.
a. If reading is the same at the sensor, replace sensor and retest.
b. If reading at sensor is correct, check wiring and ground connection at intake manifold.
13. After testing, disconnect all test equipment, reconnect all connectors (including the ECU connector) and remount all panels.
NOTE: While trouble shooting, always check the wiring, fuses and connectors for good condition and routing. Use the wiring diagrams found in ELECTRICAL DIAGRAMS to supplement your testing efforts.
Removing Ignition ECU Connector:
1. Turn ignition OFF.
2. Access ignition ECU by removing the passenger side kick panel and glove compartment.
3. Remove ECU connector by pushing out the catch and folding out the wire cluster.
4. Check ignition ECU ground connections at intake manifold. They should make good contact.
Removing Protective Cover:
5. Remove connector protective sleeve.
IMPORTANT:
Never check connections from the front. Connectors can get damaged and worsen the problem.
Check connections through the holes in the connector.
Connection pin numbers are printed on the connector side.
Checking Terminal Pins:
6. Check that terminal contacts have been pushed down evenly in connector.
7. If any connectors have been pushed down to far, poor connection may result.
Checking Battery Supply:
8. Check main power supply by connecting a voltmeter between pin 5 (red) in ECU connector and ground.
Reading: approx. 12 volts
9. If no voltage registers, check wire between ECU and in-line fuse on left suspension strut tower. Check fuse and wiring to battery (incl. battery terminals). Repair as necessary.
Checking Temperature Sensor:
10. To check the coolant temperature sensor, connect an ohm meter between ECU connector pin 2 (blue-red) and ground.
Coolant Temperature Resistance Chart:
11. Resistance depending on coolant temperature should be (also see chart):
-10°C (14°F) 8,260 - 10,560 ohms
+20°C (68°F) 2,280 - 2,720 ohms
+80°C (176°F) 290 - 364 ohms
12. If a fault occurs, measure at coolant temperature sensor to see if the sensor or the wiring is the problem.
a. If reading is the same at the sensor, replace sensor and retest.
b. If reading at sensor is correct, check wiring and ground connection at intake manifold.
13. After testing, disconnect all test equipment, reconnect all connectors (including the ECU connector) and remount all panels.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.