Volvo 900 Series Relays

Relays are arranged in a logical sequence by rows. Note that equipment level (e.g., fog lights or power windows) affects whether each location has a relay installed.

Location Function / System Note A Light Failure Monitor Large round or oval (usually red or orange). B Seat Belt Reminder Makes a clicking sound if belt is not fastened. C Wipers Controls misting function and wiper speeds. D Rear Washer Wagon models only (945/V90). E Fuel Pump Relay Most important! Usually white or blue in newer models. F Front Fog Lights Only if the car has original front fog lights. G Turn Signal Relay Controls turn signals and hazard flashers. H Temperature Warning System alarm relay (not all models). I Overdrive M46 manual transmissions or AW automatics. J Seat Heaters Controls seat heating elements. K Headlight Relay Headlight switching relay. L Central Locking Controls door motors. M Engine Control / Injectors Connected to fuel system. N High Beam High beam headlight control.

In 1994–1995 Volvo 940 models (especially B230FD naturally aspirated, Bosch or Regina), a square, low-profile blue relay is used instead of the traditional long white relay. Location: Front row, second position from the right (Location E). Failure susceptibility: Like its white predecessor, the blue relay often suffers from broken solder joints (cold solders), causing the car to stall or difficulty starting when warm.

Fuse 1: Often the main power for the fuel system passes through fuse number 1. Check it first if the pump doesn't run. Relay testing: If the car won't start, try to hear if the relay "clicks" under your finger when the key is turned to power on. If it doesn't click, the relay is not receiving control voltage or it has failed. Radio interference relay (Engine bay): Don't confuse interior relays with the black relay on the shock absorber strut in the engine bay. That is the main injector/engine control relay, and its failure also prevents the car from starting.