My father inlaw has a dodge van that is having problems starting. When starting it will crank, but will not fire. We have discovered that if you remove the 20 amp Oxygen Sensor relay, under the hood, and jump it directly to the battery, while starting if will start. The fuse appears to be good. Can the O2 sensor relay prevent the van from starting, but run after initially bypassing after starting? Any idea what it might be?
I’m having some problem with the belief that there is a 20 amp oxygen sensor relay on any vehicle. I hope there is no such thing but if it works, who cares what it’s called?
I’m trying to read a text book about computer communications. If I finish it by the year 2049 I’ll read some more stuff about cars. Good luck with your bypassing and with the phrasing of your questions.
I don’t see how this could prevent it from starting, but I think the relay is for the HEATED oxygen sensors. O2 sensors have to be pretty hot to work properly–700 degrees or so I think. The heaters built in raise the temperature much more quickly than just heating in the exhaust manifold would do. Have you tried replacing the relay or substituting another relay, such as for the A/C or something (if it fits), to see if this allows it to start?
I think when you bypass the relay, that you may be backfeeding another circuit that has elements that are common to the circuit that you’re bypassing, and that this circuit is critical to the engine starting–eg. fuel pump, ECU, etc. If all the fuses are good, both under the hood and under the dash, then I think you need to find a wiring diagram for the van and see what else is connected to this.
Probably what you’re doing when providing power at the O2 heater fuse is backfeeding power to the ASD relay. Swap that relay with another one that is not important for the running of the engine.
As Pete Peters and Oblivion mentioned what you are acually doing is backfeeding power that should come from the ASD relay. Not only does it supply power to the Secondary O2 Sensor relay but also to the injectors. So either the ASD relay contacts are bad, the control to the relay isn’t working or, fuse 11 in the panel under the hood is blown.