How the LS1 trigger works
The Gen 3 LS1 reads engine position from two places:
- Crankshaft: a reluctor wheel with a 24x tooth pattern.
- Camshaft: a half-moon style target on the cam sprocket, so the signal is high for half a turn of the cam and low for the other half.
Together they give the ECU both crank angle and which half of the four-stroke cycle the engine is in.
The crank sensor: the part that trips people up
The LS1 crank sensor is a reluctor-type pickup, but it has signal conditioning built in and outputs a clean digital square wave, just like a Hall sensor. So configure it in the ECU as a Hall Effect crank input, not a reluctor.
Edge choice matters too. On this sensor, the falling edge is the one with consistent timing between teeth, and it's the edge to use. The rising edges are spaced unevenly (that's how GM encodes position) and the Haltech Elite range can't use them.
It sits above the starter, toward the rear of the block. Pay attention to the color:
- Black sensors are Gen 3.
- Grey sensors are Gen 4, and they won't work with a Gen 3 crank trigger pattern.
If you replace the crank sensor, check the color before you fit it: a Gen 4 part on a Gen 3 engine won't give the ECU a usable trigger.
The cam sensor
The cam sensor is a conventional Hall Effect sensor. On Gen 3 engines it's mounted up high at the rear of the block, where the two cylinder banks meet.
Sensor pinouts
Both sensors use the same three-pin layout:
| Pin | Job | Haltech wire |
|---|---|---|
| A | Signal out | Yellow, Trigger + |
| B | Ground | Blue, Signal Ground |
| C | Power | Red, 12V+ |
If a sensor won't produce a signal, check the 12V supply and signal ground at pins C and B first, then the signal on pin A with a scope.
Getting it running
- Set the crank input as Hall Effect, falling edge.
- Confirm you have the correct Gen 3 (black) crank sensor.
- Crank the engine and check that the ECU sees a stable RPM and sync.
- Always confirm base timing with a timing light before loading the engine.
Need the trigger configuration screen for your ECU? Ask us and we'll send it over with advice for your build.
Related: LS2/LS3 trigger information, LS1 engine, and checking crank and cam sensors. For a ready-made harness, see the Elite 2500 GM Gen III LS1/LS6 terminated harness kit.
