850 (Fuel Gauge Does Not Operate At All Times)

1. Turn ignition on. Activate diagnostic test mode No. 3. See DIAGNOSTIC TEST MODE NO. 3 under SELF-DIAGNOSTICS. If fuel gauge indicates 1/2 full, go to next step. If fuel gauge does not indicate 1/2 full, replace instrument cluster.
2. Turn ignition off. Remove right side panel in trunk. Disconnect Black 2-pin electrical connector. See Fig 1. Connect an ohmmeter between sensor connections. Depending on amount of fuel in tank, if ohmmeter indicates 7.5-12.5 to 322.5-327.5 ohms, go to next step and check sensor ground connection. If ohmmeter does not indicate 7.5-12.5 to 322.5-327.5 ohms, replace fuel level sensor.
3. Ensure ignition is off. Connect an ohmmeter between harness connector terminal No. 2 (Yellow/Red wire) and ground. If about zero ohms are present, go to next step and check sensor signal circuit. If about zero ohms are not present, check for an open circuit in wiring between connector terminal No. 2 (Yellow/Red wire) and 30-pin connector on instrument cluster.
4. Connect voltmeter between harness connector terminal No. 2 (Yellow/Gray wire) and ground. Turn ignition on. If about 7 volts are present, replace instrument cluster. If zero volts are present, check for a short to ground or an open circuit. If battery voltage is present, check wiring for a short to voltage.

Fig 1: Locating Black 2-Pin Connector In Trunk

Courtesy of VOLVO CARS OF NORTH AMERICA.