Inductive Crankshaft Position Sensor Voltage Drop When Split Between Inputs

I'm working on a project with a vehicle using two engine control modules, which both need accurate crankshaft position signals to function. Adding a second sensor is not an option. The sensor is an inductive sensor producing a semi-sinusoidal waveform, NOT a Hall-Effect sensor.

The issue I have been seeing and have tested is that as the frequency of the inductor is increasing, i.e the vehicle RPM is increasing, the voltage applied to one of the modules is leveling off. I measured the sensor to produce a voltage of around 12VAC at ~7000rpm, however when split one of the connections measured at only 4VAC. The frequency measurements were correct for both computers, however I believe that they also use the applied voltage to determine engine speed.

I do not have any technical documentation for this sensor, as it hasn't been made public to my knowledge.

What are some possible solutions for this problem? I have considered using an opamp but am unsure how that would improve the situation.

• the sensor may be a reluctance sensor – jsotola Feb 14 at 17:22
• please draw a diagram of what you connected and how you connected it – jsotola Feb 14 at 17:25
• You are correct it is a VR sensor. I think i've figured out that the current draw is too large with both inputs over the sensor and it is clipping the voltage. I intend to put a voltage follower circuit inline on one of the signals to see if that changes anything. – Devon Freeland Feb 14 at 18:07
• With very little to go on this question begs for the inclusion of waveform pictures and diagrams of your set up. – Andy aka Feb 14 at 18:16
• This seems like a tricky problem. The two ECUs may disagree on the voltages that should be present on the input. you may need to amplifiy the signal and present isolated copies of the amplified signal to both ECUs... we need voltage measurements on both terminals of both ECU inputs. – Jasen Feb 15 at 6:31