papaford

I'm trying like crazy to start setting up my ve tables but running into snags..I noticed taking reading with tts datamaster that my intake air temp reading is -58 degrees and my computer throws code 23 (iat out of range..to low).
I checked the wires and they look OK..I changed the sensor and still get the same readings.. Any thoughts?

Grumpy

CIRCUIT DESCRIPTION:
The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM The ECM applies a voltage (about 5 volts) on CKT 472 to the sensor. When the air is cold the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. If the air is warm, the sensor resistance is l( therefore, the ECM will detect a low voltage.


MAT Sensor
Temperature vs Resistance (Approx)
Deg. F Deg. C Ohms
210 100 185
160 70 450
100 38 1,800
70 20 3,400
40 4 7,500
20 -7 13,500
0 -18 25,000
-40 -40 100,700


TEST DESCRIPTION:
Numbers below refer to circled numbers on the diagnostic chart. Code 23 will set if:

A signal voltage indicates a manifold air temperature below - 30'C (-22'F).
Boost conditions have been present for longer than 10 seconds.
Due to the conditions necessary to set a Code 23, the "Check Engine" light will only stay "ON" while the fault is present.
A "Scan" tool may not be used to diagnose this fault, due to the ECM transmitting "default" (substitute) values while the fault is present. A Code 23 will set due to an open sensor, wire, or connection. This test will determine if the wiring and ECM are OK.
If the resistance is greater than 25,000 ohms, replace the sensor.

Ed Maher

How they look doesn't matter much. If i were in your shoes i'd ohm the sensor from the ECM side of the harness. If it checks out OK, then the A/D in the ecm is bad (or you have a bad connection harness-ecm.) If it isn't OK, well then the answer should be obvious. But 'looking' at it won't help you much. Wires break internally all the time.

Morley

Also, on my TPI engine there are actually 2 connectors to that sensor, one at the sensor and another about a foot or so down the wires. Make sure that one is still hooked up and in good shape.

papaford

thanks for the help guys.. I had replaced the sensor and still got the same reading. The new sensor must be defective because I checked all the wiring and it is good.. when i put a resistor across it everything is just fine...