Volvo 850 Fuel-Pump Controller/Relay replacements



Ever struggled to replace your old fuel pump relay and wonder how many different types of relays there are? Then let's bring some light into the dark.

There are basically 2 different types of relays, the mechanical and the electronic variant. The mechanical variants can be recognized by their 4 poles, the electronic ones have 5 poles.

How relays can be exchanged with each other depends on which variant was installed at the factory. - no title specified

Factory:

Color

Type

Variant

These relays can serve as a replacement part

9441029

Pink

electronic

new

9434013

9434224

9434138

9434013

Yellow

electronic

old

9441029

9434224

9434138

9434224

Red

mechanical

new

9434138

9434138

Green

mechanical

old

9434224



If you have a 4-pole variant, i.e. a mechanical relay with 4 contacts in the base, this can only be exchanged for another mechanically relay. If, on the other hand, you have the 5-pole variant, i.e. 5 contacts in the base, then any available relay, whether mechanical or electronic, can serve as a replacement.

The electronic relays has a series resistor 20/11 on connection 87B, which is routed to connection 87A, i.e. also directly to the pump.

I haven't found any documentation about it, but my interpretation of the circuit diagram is that the pump is first controlled via the FET with the series resistor from connection 87B, and shortly afterwards from the second FET directly to connection 87A.

The idea behind this could be to lower the inrush current of the pump for the relay, when the pump has started, the full current is switched through.

My assumption is therefore that a mechanical relay does not really care about the current peak, but that an electronic component can burn out within a few milliseconds due to the short, high starting current.

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Schematic

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