Dialing In LS Sensors For Various Generations With Michigan Motorsports

When it comes to junkyard LS engines, the sky is the limit, as there were so many of these formidable powerplants produced. However, one thing that really isn’t usable from the wrecking yard — are the numerous LS sensors utilized by the Gen-III and Gen-IV engines.

While used sensors might seem like an easy corner to cut in order to save some money, these amazingly sensitive devices perform an incredibly important function in a performance LS engine, so replacing them with new pieces for your fresh build is a no-brainer.

However, there are a lot of different sensors on the market for the Gen-III and Gen-IV engines: OEM, aftermarket, economy, and expensive. In order to wade through the sea of options, we reached out to Michigan Motorsports. They not only know the right part numbers for whatever setup you’re running (a Gen-IV on a Holley Terminator X, in our case), they know what affordable sensors work, and which sensors it’s worth spending a little more on. They guided us through LS5.0’s sensor journey and sorted us out.

Gen-III Vs. Gen-IV LS Sensors: Don’t Mix Them Up

When it comes to the two different generations of LS engine, choosing the correct LS sensors can be tricky, because the number of sensors used is the same, but they aren’t the same sensors exactly, as Michigan Motorsports’ Dan Baber explains. “The crank and cam sensors are (physically) different between Gen III (24x) and Gen IV (58x). Also note that 24x cam and crank sensors are 12-volt, while 58x cam and crank sensors are 5-volt. This actually doesn’t matter much in Holley since the switching voltage the ECU is looking for is around 3 volts, so you can make them work if you just repin the harness, but on factory ECUs, that matters a lot.”

One thing that is done is to run a Gen-IV engine with a Gen-III ECU and harness. But, Baber notes that conversion is only possible going in one direction. “Currently, there is no way to get a Gen-IV PCM to run on 24x that I’m aware of. To run a Gen-III PCM on a 58x engine, you can use the Lingenfelter 58x to 24x conversion box.”

Baber continues on the differences between generations of LS sensors, “There are three variations of oil pressure sensors for different years/models, which all use different connectors, but they aren’t Gen-III or Gen-IV specific. Coolant temperature sensors are the same on all engines. Some early Gen-III cars have a separate IAT sensor, but most LS engines have the IAT built into the MAF. Then, there are several different MAF sensors depending on year and model.”  

Whether you start with a Gen-III or Gen-IV engine largely depends on your budget, power goals, and whether you are planning to replace things like the pistons and rods or use the factory ones. Baber explains, “Gen-III engines tend to be cheaper than Gen IV. If you are going to replace rods and pistons, then it really doesn’t matter that the Gen-III rods are a little weaker. For low-power builds, they are equal, and for high-power builds where the rods and pistons will be replaced, they are pretty equal. In between is where a Gen IV can be worth the extra money. Also, Gen-IV engines for the most part came with better cylinder heads from the factory, especially on 6.0L/6.2L. Again, though, that doesn’t matter if it’s just a cruiser or if you will be replacing the heads anyway. In between where you want to use factory heads but make some strong power is where it can be worth spending the extra money  for a rectangle port version of the 6.0L or for a Gen-IV 5.3L/4.8L with the 243/799 heads.”

So, with that in mind, we started out by diving into sorting out the sensors for LS.0, specifically. Remember, LS5.0 is a Gen-IV LY2 4.8-liter-based engine, and we’re using a Holley Terminator X with the Gen-IV truck engine harness option from Holley EFI.

Oil Pressure Sensor

For both the Gen-III and Gen-IV LS engines, the oil pressure sensor is located on the back of the valley cover. “The 12677836 part number is the only OEM sensor that has the same connector on it as the Holley harness,” Baber says. “That sensor will work on all Gen 3 and Gen 4 LS engines without needing adapters like most aftermarket 1/8npt sensors would and has OEM reliability.” 

We used: GM P/N 12677836

Coolant Temperature Sensor

The factory Coolant Temperature Sensor is located in the driver’s side cylinder head, near the front of the head. One thing to note about coolant temperature is that it is a fairly slow-changing channel, and as such, really doesn’t benefit from a high-end, fast-reacting sensor. “The OEM sensor works great for CTS. There’s really no advantage to going aftermarket, in my opinion,” says Baber.  Since these are the same across all the LS engines, as long as it has a factory part number, you’re good to go.

We used: GM P/N 12608814

Crank Position Sensor

Both generations of engines have the Crank Position Sensor in the same spot, but for easy identification, they are different colors, because the different generations use reluctor wheels with a different number of teeth. The Gen-III crank position sensor is black and is designed to work with a 24x reluctor wheel. The Gen-IV sensor body is gray and is designed to work with a 58x reluctor wheel.

“The connectors on the two sensors are the same, just with different slot keying. So, if you trim the keying tab you could plug them into each other, but you want to just get the correct sensor for the harness in most instances. The 24x and 58x crank sensors physically look the same, just 24x is black and 58x is gray from the factory. Note that a couple of years ago, GM started making the 58x sensors black as well, though, so unless the engine still has the original OEM sensor in it, you can’t 100 percent trust using color alone to identify them. Some aftermarket parts-store type sensors may not stick to the GM color coding either,” Baber warns.

We used: GM P/N 12703627

Camshaft Position Sensor

The camshaft position sensor is also different between the generations, as the 24x reluctor system uses a 1 single cam position signal, while the 58x systems use a four-pulse magnet. The sensors are also installed in significantly different locations; the Gen-III is on the back of the block, and the Gen-IV is on the front timing cover.

“For the cam position sensors, the 24x Gen-III LS sensors are physically different (a tall/long black sensor that goes in the rear of the block) from the 58x Gen-IV LS sensors, which are a short tan sensor that goes into the timing cover. A few oddballs (early LS2 with E40 PCM, as well as a few LH6 midsize SUV and early LS2 CTS-V/TBSS) are 24x with the cam sensor in the timing cover. Those engines use the same part number cam sensor as Gen-IV,” elaborates Baber.  

We used: GM P/N 12633906 (front cover with the sensor included)

Knock Sensors

While knock sensors might not seem important, besides being able to save your engine from a bad tank of gas, if they start malfunctioning, they can be a giant pain. We’ve seen issues when people use poor-condition junkyard knock sensors — as well as cheap new generic replacements — having to deal with “ghost knock.”

“We see the same,” says Baber. “Really, you want to just stick with OEM for the knock sensors. Gen-III OEM sensors are pretty expensive so people get more tempted to go with cheaper options there. The Gen-IV GM knock sensors are still pretty cheap so there is no reason to mess with aftermarket replacements, and in general, we rarely see Gen-IV sensors go bad. The Gen-III sensors tend to fail due to water collecting in the recess where the knock sensors sit under the intake manifold.”

We used: GM P/N 12623730

Throttle Position Sensor

Critically important to smooth drivability, the throttle position sensor is an incredibly important piece of the puzzle with the ECU. “Aftermarket TPS sensors are very prone to failure, and in most cases, it will be intermittent small glitches just in certain parts of the sensor range that are hard to diagnose,” says Baber.

“As far as I’m aware, all aftermarket brands of mechanical throttle bodies, up to 105mm, use the 1998-‘02 LS1 Camaro-style TPS sensor. On some crazy huge race throttle bodies, they go to different style TPS, but nobody really uses those on LS engines.” With that advice, we chose a GM for our 105mm Holley EFI throttle body.

We used: Delphi P/N SS10382

Idle Air Control Valve

Idle air control valves are only present on cable-driven throttle body LS applications, as they regulate the amount of air bypassing a closed throttle body blade. On drive-by-wire applications, the ECU adjusts the amount of air by opening and closing the throttle itself.

“Aftermarket replacement IAC valves tend to have issues more than the GM ones do. GM IACs are hard to get anymore, so the next more reliable option seems to be the Delphi sensors,” says Baber. “Holley has their own IAC as well that a lot of people use, though I’m honestly not sure how reliable those are compared to Delphi.” 

We used: Delphi P/N CV10017

Intake Air Temperature

This is a bit of a minefield for aftermarket setups, as a good chunk of LS factory-ECU setups have the IAT sensor incorporated into the mass airflow sensor. So, switching to a standalone IAT sensor can be confusing, since there are a lot of different sensors that not only vary pretty heavily in price, but also all look very different.

“For naturally aspirated and mild boost builds, the GM LS1 press-in IAT sensors work fine and have the same connector as Holley,” explains Baber. They can be pressed into a silicone CAI tube or into a metal pipe with an appropriately sized grommet. I personally just used the grommet method on my C6, and it has stayed in for 10 years with 15-20psi of boost, but I fit it pretty tight.”

“Most people with fabricated intakes or boosted builds want a thread-in sensor, though, or people who want to thread them right into the back of aftermarket aluminum intakes want threaded as well. For those, you can use earlier GM 3/8-inch NPT sensors from a third-gen Camaro, etc. You just want to make sure to get one of the later versions with the exposed element style sensor, not the earlier ones with a solid tip, like a coolant temp sensor; they respond much slower.

“On boosted applications, a lot of attention has been pointed towards how slow the factory sensors react to temp rise, so a selling point for some of the aftermarket sensors has been the faster response rate, and it’s also nice that some of them can be had with smaller 1/8-inch or 1/4-inch NPT threads. Since the vast majority of LS engines had no IAT sensor from the factory, the IAT is the most popular sensor to need to get when switching to aftermarket EFI, such as Holley, that no longer uses the MAF.”

For most projects response time of the IAT sensor doesn’t really make a difference, though. Baber feels that’s where the end-user needs to make the choice as to whether they want to spend extra money or not. “With high-power boosted builds without intercoolers, you can also run into cases where you will exceed the temperature range of the OEM sensors, so some aftermarket ones with a higher temperature range can be needed. But the GM sensors are fine to 250 degrees, so not many people are up above that range with street cars.”

We used: GM P/N 12160244

Final Thoughts on Sensor Selection

At the end of the day, there are a lot of options for sensors for the LS engine, ranging from “value” options all the way up to ultra-premium, almost lab-grade sensors. What’s “best” for the average person falls somewhere in the middle.

“Stick to well-known name brands if reliability matters more than budget, especially for mission-critical sensors. In general, when it comes to aftermarket sensors, you do tend to get what you pay for (higher cost sensors tend to be more reliable than lower cost ones). Sometimes OEM sensors can cost less than the aftermarket ones, though, while still being more reliable. 

“Try to avoid parts-store replacements if you have the time available to get OEM. In a lot of cases, you can get OEM GM sensors from online retailers for the same or lower cost than inferior quality parts store aftermarket replacement sensors,” concludes Baber.

He also adds something that we didn’t consider on LS5.0 because it will likely be monitored by the engine dyno’s sensor suite: fuel pressure. “Anybody switching to Holley will want to get a fuel pressure sensor since the harness comes pre-wired for one,” Baber relates. “The [ECU] system doesn’t actually use the fuel pressure for anything in the tune, though (it’s just there for logging or to display on your dash), so it’s not a big deal to go with a cheaper brand there if somebody wants to, since a sensor failure won’t leave them stranded or hurt the engine. Though if you end up needing to buy two of the cheap sensors, you would have been better off paying for something a little better from the start.”