The General Motors LS3 crate engine has 10 engine harness connections on the engine block:

  1. coolant sensor – 2 pin
  2. engine oil pressure sensor – 3 pin
  3. crankshaft position sensor – 3 pin
  4. knock sensors (2) – 2 pin
  5. camshaft position sensor – 3 pin
  6. manifold absolute pressure (MAP) – 3 pin
  7. mass air flow (MAF) – 5 pin
  8. fuel injectors (8, 4 on each side of block) – 2 pin
  9. ignition coil blocks (2) – 8 pin
  10. electronic throttle control – 6 pin

There are four engine harness connections to related components:

  1. vehicle speed sensor (VSS) – 2 pin on the 4L65e transmission
  2. oxygen sensors (2) – 5 pin on each exhaust manifold
  3. accelerator pedal sensor – 6 pin on the pedal assembly
  4. alternator control connector – 1 pin on the alternator

There are 7 tube openings on the block:

  1. coolant steam vent (to Radium reservoir)
  2. crankcase vent dirty air PVC vent (capped)
  3. clean air PVC intake (to MAF intake)
  4. EVAP emission purge solenoid (removed) and dirty air vent (capped)
  5. vacuum port for brake servo
  6. fuel rail 3/8″ intake tube (converted to -6AN fitting)
  7. fuel rail end port (for fuel pressure gauge)

In addition, the GM Supermatic 4L65E transmission has a round plug connection from the transmission harness.

Block connectors and openings

Here is a visual guide to some of the connectors and tube openings on the LS3 block.

Coolant sensor

LS3 coolant sensor on driver side

HDX coolant sensor location on passenger side

The factory sensor, located on the driver side just in front of the exhaust manifold, must be enhanced by a special Dakota Digital SEN-04-5 sensor designed for the HDX dash display which is installed on the opposite passenger side of the block.

Coolant sensing is required for the LS3 ECM in order to operate the cooling fan, so two sensors are actually required, one for the HDX and another for the LS3 ECM.

The SEN-04-5 sensor has 1/8″ NPT threads and Dakota Digital supplies a 1/8 NPT-to-12mm bushing with a crush washer that mounts into a plugged port on the rear passenger side of the block. Wiring from the SEN-04-5 goes directly to the HDX through the bulkhead and is not incorporated into the LS3 engine harness.

Engine oil pressure sensor

Oil pressure (white) and brake servo vacuum (red)

The HDX display also requires a special SEN-03-8 oil pressure sensor. However, unlike the coolant sensor, the LS3 ECM does not require oil pressure data for operation.

Thus, the Dakota Digital SEN-03-8 sensor can simply replace the factory original one, and the oil pressure sensor extension of the factory LS3 harness will not be used. The SEN-03-8 is wired directly into the Dakota Digital HDX unit. Dakota Digital supplies a 1/8 NPT-to-16mm bushing that fits into the factory port.

Engine vacuum supply for the brake servo is located by the oil pressure sensor.

Knock and crankshaft position (CKP) sensors

Knock and camshaft position sensors

Two knock sensors on opposite sides of the lower engine block protect the engine by enabling the ECM to change ignition timing. The harness leads are heat protected since they run close to the exhaust manifolds.

The single crankshaft sensor is at the rear of the lower part of the passenger side block.

CKP (grey) and knock (black) sensor connections


Camshaft sensor

Camshaft sensor

The camshaft sensor (CMP) itself is located at the front of the engine block on the driver side near. But to make access easier, an extension harness bends around the harmonic balancer and terminates near the bottom of the block on the right side (when facing the engine). The harness connector thus points down.

The CMP signals the ECM about the camshaft position and operates in sync with the CKP. The CMP determines which injector to fire. Both the CMP and CKP are essential elements of engine operation.

Camshaft sensor and harness extension


Fuel/air connections

Passenger side coil block and injectors

The manifold absolute pressure (MAP) and PVC air inlet to the mass airflow (MAF) sensor all help the fuel injectors and coil blocks operate efficiently. There are eight injector connections and two coil blocks.

The EVAP purge solenoid is not used (it is shipped with the LS3 crate engine).

MAP, PVC air inlet, and injector connections


Electronic throttle control

Throttle control connection

A black connector on the passenger side of the throttle body attaches to the electronic throttle control of the engine harness.

The engine harness has four other extensions that connect to related components: the exhaust manifolds on opposite side of the block, the front-mounted alternator, the accelerator pedal in the driver’s foot box, and the vehicle speed sensor (VSS) on the transmission. The VSS is required for LS3 “Connect and Cruise” mating to the transmission.

Mass airflow (MAF)

The throttle body sits at the top center of the LS3 engine and points slightly up. The wide circular opening attaches to a long “pipe” with the MAF sensor embedded on the left side and a port for “clean” PVC air on the right. The MAF housing pipe then connects to an over-the-radiator air filter.

MAF sensor and harness connection

PVC clean air vent into the MAF housing

Test fit of MAF, air filter, and radiator


LS3 tube openings


4L65e transmission connections

The vehicle speed sensor (VSS) extension on the LS3 harness connects to the rear of the 4L65e transmission. The main plug from the transmission harness (separate from the LS3 engine harness) connects to the circular mount on the passenger side of the transmission.