Real Fiero Tech

My car has a few small issues that I was going to start working on. The TPS and the IAC are both throwing SES lights for low voltage, and I'm getting an SES for low temperature on the Coolant Temp Sensor. The car won't idle to save its life.

So, if anyone would please do this, it'd help A LOT. Remove the 3 connectors for the IAC, TPS, and CTS. All 3 are right in the same area, and easily accessed. Then, looking at the plugs with the snap clip on top, let's call the pins A, B, C, and D. Can you all trace these wires to the ECU, and tell me which pin they go into?

I have the schematics and know which IAC wires go into which pin, but the I don't have a pinout for the IAC. So I don't know which one should be reference, ground, etc.

So this is what I want to know:

IAC: A to D1, B to D2, C to D3, D to D4
TPS: A to D1, B to D2, C to D3
CTS: A to D1, B to D2

Now of course they don't all go to the same place, the D1, D2, and D3 was for example. Thanks A LOT GUYS!!!

The plugs actually do have letters imprinted on them. Listing the actual letters would probably help. If the wiring is from some stock car, the color codes would be easier to match up.

whipped wrote:The plugs actually do have letters imprinted on them. Listing the actual letters would probably help. If the wiring is from some stock car, the color codes would be easier to match up.

I'll check them again, but didn't see them the first time.

The colors are aged indistinguishable from each other.

IAC works on PWM, there's no reference.

If you're getting a large voltage drop, sounds like you have a short to ground somewhere. Check ALL The sensors that come off the 5v voltage bus, since a short on one can throw the others out, too (only one 5v regulator, IIRC?)

To rule out something with your ECM, check for voltage with the key to ON at the reference pins. Check this right at the ECM, and then compare voltage apparant at the sensor
:
You should be seeing 5.0v (+/- 10%) at the ECM, and the voltage at the sensor should be well within 5% or so of that voltage.


MAP sensor:
ECM: Pin C7
Sensor: Pin "c" (grey)

TPS:
ECM: Pin C12
Sensor: Pin "A" (grey)

CTS:
ECM: Pin C16
Sensor: Pin "B" (yellow)
*** Disconnect sensor when taking reading, as the thermistor will cause a voltage drop.

IAT:
ECM: Pin C4
Sensor: Pin "B" (tan)
*** Disconnect sensor when taking reading, as the thermistor will cause a voltage drop.


If your voltages are out of whack, you've got trouble. If the reference is low, disconnect the harness and check for path to ground through each circuit. With the IAT and CTS disconnected, there should be NO continuity.

Ok I checked the voltages today.

At the ECU, I'm getting 5.03v at all 4 terminals (C4, C7, C12, C16).

At the connectors to the appropriate sensor, I'm getting 5.02v at all 4.

So all of this looks normal. Maybe one (Or more) of the sensors is bad?

I reset the ECU by unplugging the battery for a few minutes, and plugged it back in, then I started the car. It looks like the Overtemp lamp and the SES lamp come on at the same time, about a second or two after startup. I read the codes, and only got a 15 and 22. 15 is Coolant Temperature Sensor-Low temp indicated, and 22 is Throttle Position Sensor, low voltage indicated.

Maybe one of these sensors is bad, and is fucking up the other? I'll check my 5v references, this guy might have tied them together for some reason.

Could be...

Obviously your reference wires are OK then.

The 2 next culprits will be the ECM grounding to the engine. Double-check those, and test resistance across the sensor grounds to the neg post on the battery. You should be seeing LESS than 3-4ohms.

Once you check that, also make sure the ECM grounds are showing 3-4ohms or less from the grounding pins.

So:

Sensors:

MAP:
Sensor Ground: Pin "A" (black)
ECM Ground: Pin "C5" (black)

CTS:
Sensor Ground: Pin "A" (black)
ECM Groung: Pin "C10" (black)

IAT:
Sensor Ground: Pin "A" (black)
ECM Ground: Pin "C5" (black)

TPS:
Sensor Ground: Pin "B" (black)
ECM Ground: Pin "C10" (black)


If the grounds check out, you need to check the signal wires. With the engine running, probe the outputs of each sensor for voltage; all of them should be at or less than the 5v reference (check it to make sure it doesn't change while running).

MAP:
Sender: Pin "B" (lt. green)
ECM: Pin "C22" (lt. green)

CTS: Probe the reference wire; the ECM measures voltage drop across the thermistor to ground (just like a multimeter). With the sensor disco'd you'll see 5v, plugged in, it'll be less.
Sender: Pin "B" (yellow)
ECM: Pin "C16" (yellow)

IAT: Same as CTS; prove reference wire, look for voltage drop.
Sender: Pin "B" (tan)
ECM: Pin "C4" (tan)

TPS: Voltage will vary with throttle position; 5v disconnected, varied when plugged in.
Sender: Pin "C" (dk. blue)
ECM: Pin "C15" (dk. blue)



Try that.

Oh shit... I'd forgotten about that...





YOU CHEAP FUCK

What is BTFM?

All I'm getting is "Beats the fuck out of me," which I don't think is possible with Will...

Buy The Fucking MANUAL!

I already have it. And it's done me no good, besides explain what my SES lights are, which can be found even faster online.

most public libraries have service manuals & copy machines.