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 MANUALSVOLVO1991740 BASE, 4D WAGON, AUTOMATIC, AW70LREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODESSELF-DIAGNOSTICS - TURBO SYSTEMCONTROL FUNCTION NO. 3TESTING TURBO SYSTEM COMPONENTS
1991 Volvo 740 Base, 4D Wagon, Automatic, AW70L
Testing Turbo System Components
1991 Volvo 740 Base, 4D Wagon, Automatic, AW70LSECTION Testing Turbo System Components
- Turn ignition on. Locate diagnostic unit and remove its cover. Connect selector cable to socket No. 5. Depress push button 3 times. Each time the button is depressed, it should be held for more than 1 second and less than 3 seconds.
- While LED flashes, the cooling fan, turbo control valve and A/C blocking relay should operate. Check by listening or feeling component when it is activated. If turbo control valve does not work, go to step 3). If A/C blocking relay does not work go to step 4). If cooling fan does not operate, check both cooling fan relays. Connect voltmeter between turbo control unit terminal No. 4 and ground. Then between terminal No. 5 and ground. In both cases, reading should be 12 volts.
- Connect ohmmeter between turbo control unit terminals No. 1 and 3. Resistance should be 11 ohms. Replace control valve as necessary.
- Turn ignition on. Connect voltmeter between turbo control unit terminal No. 6 and ground. Reading should be 12 volts. Turn ignition off. Install turbo connector. Start engine and turn A/C on.
- After compressor engages, press accelerator pedal to floor for a short time. Compressor should disengage when throttle is fully open and engage again when throttle closes slightly from fully open position. Replace A/C blocking relay as necessary. Turn ignition off.
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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.