Nissan CAS Wiring

I watched the most recent webinar on wiring fundimentals and during the Q&A there was a question that brought up the subject of sensor grounds and chassis grounds. You guys touched on the fact that both SR20 and RB Cam angle Sensors use a chassis ground rather than a sensor ground in the factory engine harness. I wasn’t able to catch the whole explanation in the webinar. So my question is: Was there a reason Nissan chose to ground the sensors this way, and is it the best way to do it. Or, is grounding the CAS with a sensor ground a good/better option?

G'day Alex.

I'm not sure the reason Nissan chose to do this, but I would think its because it worked for the OEM setup, and was probably cheaper to manufacture the CAS's this way. They're an optical sensor, so need a power and a ground for their internal circuitry, but it would have been nice if they had a separate ground reference pin also.

If you haven't seen it, we struck some juicy grounding issues on an S14 earlier this year and I wrote an article on the process we went through to solve it:

https://www.hpacademy.com/technical-articles/staying-grounded/

The CAS wasn't the problem in the end, but it did play a supporting role :-).

Thank you for the quick response. I read the article and it was definitely filled with some very interesting information, but I don’t feel like it really helped answer my question.

Main main concern on the topic is that since the SR20 CAS is an optical Hall sensor, it may draw more current to power it up than a more conventional hall sensor. As a result, if the CAS was grounded using a sensor ground pin at the ECU, could it be to much current for the ECU?

At the same time though, if the scenario above is not the case, would using a sensor ground pin at the ECU help isolate the circuit and protect the cam/crank signal from potential noise or back feeding current as opposed to using a chassis ground?

G'day Alex.

The problem is that you don't have a choice where the device grounds. You can't solely ground it to your sensor ground circuit, as the CAS grounds through its body to the engine block also. Infact, if you connect the ground pin on the CAS connector to your sensor ground circuit, this will connect your sensor and power grounds at the CAS body, something we ideally want to avoid. What I mean here is that the ground pin on the CAS connector is connected internally to the body of the unit.

They don't have a huge current draw, so there isn't going to be a problem with them passing too much current to the ECU. If this was to happen, the voltage at the ECU would rise slightly, and the excess current would then ground out through the engine block, till an equilibrium is reached.

So just to be absolutely clear, if an aftermarket harness on the SR20 were to have the CAS grounded to an ECU Sensor Ground pin, it should definitely be changed to a chassis ground?

Also if it was a more conventional hall sensor like a Honeywell GT101, that still calls for 12v power, would sensor or chassis ground be the best choice?

If I was having problems, and logging strange sensor offset issues, then yes, I would try switching it to the chassis ground.

Yes, I typically ground GT101's to the sensor ground, as they are an open collector design, they connect their signal wire to their ground wire when they detect a tooth. You need a pull-up on the signal line to give it a default value when the sensor is not detecting a tooth, this is usually enabled in software inside the ECU. The ECU usually pulls the signal up to its 5V sensor supply. The value of this pullup resistor is what largely determines the current that passes through the signal ground back to the ecu, but will be a few milliamps at the most. Also, GT101's can accept a power supply anywhere from 4.5-24V, so you can power them from your sensor supply without any issues. This isn't the case for all hall/optical sensors though.

As an aside, I don't like using GT101's as engine speed sensors for any trigger wheel that has missing teeth. Often the change in flux generated by the tooth that ends the gap is much larger than the rest of the teeth which are evenly spaced. The GT101's have an internal feedback loop that adjusts their trigger levels, so what you end up seeing is all the teeth are read fine until the tooth that ends the gap comes past the sensor, the large signal this tooth creates causes the GT101 to adjust its internal trigger levels, and from then on it misses all the other teeth, only ever seeing the tooth that ends the gap! The particular situation I struck this on was a 60-2 wheel on the crank of a C20XE/X20XE engine. They are great for regular tooth wheel patterns though, and wheel speed sensing from ABS rings.

That’s fantastic information thank you!

I’m asking theses questions because on my personal SR setup, Ive switched to a Tarrks 24 tooth(no missing teeth) crank trigger using a GT101 Hall. I’m still getting my cam signal off the stock CAS that has a AEM trigger disk installed inside it. The ECU is an Infinity 506

At the moment I’ve used the wiring normally ran to the stock CAS and made a sub harness that splices the power and grounds to both sensors and runs the signal wires respectively. With that said, at the moment, both the stock CAS and the GT101 Sensor are grounded to chassis ground.

Is it ok if I leave the GT101 grounded to chassis, or would you highly recommended that being changed to sensor ground?

Also I was considering switching to the taarks came sync kit that just provides a home signal and getting rid of the stock CAS all together. Which then since both the cam and crank sensors would be more conventional style hall sensors, I would re-splice the current single ground supply at the ecu connector from chassis ground to sensor ground.

If you're not currently getting any trigger errors, then you'll be fine to leave the GT101 on the power ground circuit. I like the look of the SR trigger sensor systems that remove the CAS/Distributor altogether, very tidy... But if your current system is working fine, you're not likely to gain much from switching to one. Pulling just the cam signal from the OEM CAS is pretty reliable.