I picked up a 98 Volvo Autocar and it seemed to run well but was filthy. I cleaned it up a bit and found what looked to be a leaking gasket on the oil pump. I took it off, made a gasket and threw a bead of silicone around it, then I put it back. The leak was fixed but a check engine light came on. Code 121 (position sensor). It ran fine but i still needed to fix the check engine code. I replaced the position sensor (which is right behind the oil pump)with a new one and now not only is the code still on but it literally wont run. Its firing is all messed up. The plug looks fine. I cleaned it. I put the old sensor back in but it's still messed up. It's as if it's trying to run on 2 cylinders. Can anyone help me? Thanks.
First, what brand of position sensor did you buy? Second, is it plugged in correctly? Third, the female connection on the harness-are the wires and insulation ok. I'm leaning toward electrical problem at the connection, plus the fact those wires get oil soaked and insulation goes bad in that area.
I bought it off amazon (brand china?) It's plugged in correctly (I had to of managed to get it right 1 out of the 10 times I tried it). The plug from the harness definitely was saturated in oil and filth. I cleaned it off but I couldn't find any brake cleaner. I used air and a pick. I'm hoping it's an issue at the connection.
Check to make sure a pin in the engine side of the plug hasn't pushed out of place.
Could moving the crank manually effect the position sensor? It was moved when the oil pump was out.
No. Check the harness, moving it around may have shorted it out or broke a wire.
I spent a good 3-4 hours checking the harness. I cut the plug and wired it directly to the sensor. I'll keep checking the wiring and I'll get a new plug to wire it back. Where do I start looking if it's not wiring?
Does the nose of the sensor show any mechanical damage? Rubbing, etc? Its weird that you get this code after removing and replacing the oil pump. Oil pump drives off the cam drive gear and the sensor picks up off the back side of the cam gear (notches). And you are absolutely sure the sensor is bottoming in its bore? IIRC that has to be screwed in with a really funky wrench.