Any questions you have before you begin buying, building and installing.
By gc1066
I have just picked up a UA4C, the pin out for the 22-pin plug is here

Something daft is confusing me...the wiring for the IAT and CLT sensors. Taking the CLT as an example the UA4C pin out states:
• pin 3 : "Coolant temperature sensor 0-5v return (2 wire sensor also fed 5v)"
• pin 8 : "5v for sensor reference (IAT, CLT, TPS)"
For my build the IAT and CLT are simple two wire sensors, I had expected to put one wire to sensor ground and the other to the ECU to read the resistance change, as per the Speeduino analogue sensor wiring schematic

The UA4C pinout indicates that I should instead connect one CLT wire to the 5v reference via pin 8 and connect the other to pin 3 - am I reading that correctly?
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By jonbill
Yeah, I'd read that the same as you. But the wiki speeduino docs are correct. Connect one wire of the IAT and CLT sensors to ground and the other to pins 2 and 3.
(the 5v reference is used for TPS and perhaps some other things)
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Yes, that's a bit confusing and he should re-word that. Also confusing that if you power it up, the CLT and IAT pins will have 5V on them. :? They are biased pull-up circuits, so 5V is already injected into the circuit internally (not separately) and the sensor variably grounds that small pullup, leaving a lower voltage (0-5V) for the ECM to read.

Don't let other readings fool you either, such as the injector terminals showing 12V at power-up. This is only a back-feed of power for the LEDs with little current, so the LEDs light when the ECM grounds each channel. It all makes sense when you look at the schematics, but can be very confusing at first. :lol:
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