LS Sensors - what they do and where they are

[cebra]

I am doing a lot of research for my swap as I am a bit data driven. I have attached what I can find as far as the sensors on the LS and what they do/where they are that may be useful to someone. Please add or modify as you see fit and I will edit this. Note this isn't technically what the sensor measures as you can get that from the name of the sensor, this is the information I have gathered on what data the sensor gathers and what the ECM does with that information. Such as the fuel sender measures the fuel level is true but the float lifts/drops and as the arm moves it provides contact with a variable resistor that lets a certain ohm of ground current to the fuel gauge to move the needle. This was important information for me to know when choosing a sender for my Wrangler tank...I needed one with the correct arm travel/depth, locking ring, and ohm resistance. I went with a 93 S-10 sender and it fit the bill.

1. Mass Air Flow (near air filter box) - monitors air for fuel MAP
2. Air Intake Temp (near air filter box) - aids in timing/fuel MAP
3. Idle Air Control (throttle body) - controls air flow for idle
4. Throttle Position (throttle body) - monitors air intake into engine for timing/fuel MAP
5. Manifold Air Pressure (intake manifold) - measures air pressure for fuel MAP
6. Cam Position Sensor (engine rear) - measures engine firing for ignition timing and injector pulse
7. Crank Position Sensor (engine near starter) - measures engine speed for ignition timing and fuel MAP
8. Knock Sensors (2 under intake manifold) - look for knocks from pre-detonation to adjust timing/fuel
9. Coolant Temp (DS cylinder head)- measures temp for ECM startup mode, cooling fans, and gauge
10. Oil Pressure - (rear of engine behind intake) measures oil pressure for gauge (see BR3W CITY Notes below)
11. 02 Sensors (2 before and 2 after cat) - Upstream before cat monitor A/F ratio and adjust ECM, Downstream after cat are to bust you during inspection
12. Vehicle Speed Sensor (inside of trans) - provides "speed" to gauge, aids in fuel MAP, needed for cruise control

Good links on sensors (less disregard the notes stating the oil pressure sensor will shutdown motor

http://my.prostreetonline.com/2013/0...to-swap-a-ls1/

https://www.hotrod.com/articles/taki...s-engine-tick/

https://www.ls1.com/forums/f6/list-s...hey-do-159572/

[95 S_Trucker]

I don’t think any of those descriptions are completely accurate. I am not trying to be rude. I don’t know how else to say it.

Mass air flow sensor: measures the volume of air entering the engine

Air intake temp sensor: measures the temperature of the air entering the engine

Idle air control valve: controls the amount of air entering the engine when the throttle is closed(only installed on drive by cable engines)

Throttle position sensor: measures the angle of the throttle

Manifold absolute pressure sensor: measures pressure(or vacuum) of the air in the intake manifold

Camshaft position sensor: measures camshaft position

Crankshaft position sensor; measures camshaft position

Knock sensors: measures spark knock

Coolant temperature sensor: measures coolant temperature of the engine

Oil pressure sensor: measures engine oil pressure

Oxygen sensors: measures unburned oxygen in exhaust

Vehicle speed sensor: measures vehicle speed.


Sensors by themselves are not able to make adjustments to the engine. The pcm uses the info it gets from the sensors to make adjustments to idle speed, injector pulse, and ignition timeing.

The knock sensors will not shut the engine down. The pcm uses the info it gets to retard/advance ignition timing. It will not cause the pcm to adjust fuel injector pulse.

The oil pressure sensor will not shut the engine down. You can unplug the sensor and you can start your engine and run it. The afm(only if your engine has it)will be disabled if the pcm doesn’t see oil pressure.

[cebra]

I understand the sensors provide data to the ECM to make the necessary adjustments for air/fuel and timing. I was trying to provide a "what the sensor provides to the ECM and what the ECM does with this information" as throttle position sensor measures throttle position, camshaft position sensor measure cam position is true but I was more trying to determine what the ECM does with the input from the sensor. I have read quite a few times that the oil pressure sensor shuts down the engine, not 100% sure because internet but I read it a lot on the Silverado forums where the sensor fails and people get stuck on the side of the road but yes you can convert to mechanical gauge and the engine will run...it just loses the dummy functionality. Mainly I was trying to provide the information needed to determine what sensor issue you may have if you have X issue as chasing OBD2 codes is a bit of a waste of time as if you throw a MAF or Upstream O2 code it could be a handful of issues. I believe we are looking at it from a couple different angles but don't dispute your inputs, the manifold air pressure sensor does measure manifold air pressure, etc. I did learn some things from your post such as IACV is only on cable throttles so appreciate it.

[BR3W CITY]

For fun, knock sensors technically don't measure spark knock. They measure all knock. You can ping you motor with a hammer and watch it log on the knock sensors. Burst knock vs spark knock vs mechanical knock.

Flex fuel sensor, sits in line with the fuel feed, measures ethanol content of fuel by measuring the capacitance using an a/c current across the fuel stream.

ISS/VSS/OSS - the various input and output speed sensors. On LS motors they don't really read speed, they read reluctance (output speed may differ from input speed), and use that value with the tire size value in the PCM to calculate speed. The ISS/OSS can differ to measure loss/slip. This is also why you'll see them sometimes compare these values to wheel speed (ABS ring speed) for traction control.

Probably best to define WHICH gen we're talking about here. Sensor locations and ways they function change GenIII-GenV.

[cebra]

I did not know that about the knock sensors, it makes sense though as they are almost like O&G downflow vibration sensors...pretty cool. What gens have the flex fuel sensor? I didn't come across that in my research, is it needed for a gen 3? I found a couple related articles:

https://www.hotrod.com/articles/taki...s-engine-tick/

https://www.ls1.com/forums/f6/list-s...hey-do-159572/

[cebra]

I was aware of that about the speed sensors. I used to tune standalone ECM's for Hondas back when I was into that (had a S2000 with ITB's and a Civic with a turbo CRV swap that required a lot of fiddling regularly) so even though the sensors are 90% the same I want to do a lot of research before jumping into HPTuners on my LS.

[BR3W CITY]

Flex fuel started late genIII, I believe after the trucks all went returnless fuel. Its not a necessary component, unless you actually want to use flex fueling.

The oil pressure sensors on Gen III only trigger dummy lights and cannot affect the running of the motor.

Gen IV has a functioning PID for oil pressure and can log an actual value.

GenIII also has an oil level sensor which doesn't actually read level , only a make or break point. Completely useless.

Easiest way to do this BTW is just download the factory service manual, hit CTRL+F and then look at every result for "sensor".

[cebra]

I am glad I created this, went back and looked through this once my LS was in and I was having issues and figured out it was the TPS.