Need help with electrical gremlin, can anyone test something for me?

[1990stanggt]

Hey guys, I'm trying to track down an electrical problem and am working with the iat2 sensor right now. I was wondering if anyone could verify that power should flow THROUGH the iat2 sensor. I can jump the plug with a piece of wire and get juice to both wires (using a test light). However, plugging in the sensor, I don't get juice to the 2nd wire. I have two sensors that I have tested it with and neither of them will let power flow through to the 2nd wire. Can anyone verify for me that there SHOULD be power flowing through the sensor? It seems to me like the sensor is supposed to measure air temp by the variation in voltage that gets through the sensor, based on air temperature, however, in my case, NO voltage flows through.......maybe I just happened to buy a bad sensor as well? Can anyone help with this?

 

[1990stanggt]

Bump for the night crew.......I can't really move forward with the truck until this is figured out and fixed, so anyone who may have some advice please let me know! :beer:

 

[JollyGiant]

The iat sensor is a variable resistor. As the temperature rises it will allow more current to flow.

 

[1990stanggt]

Ok so there definitely should be at least some current flowing through it at ambient temperature, and according to my test light (unless it's not enough to light it) there is NO current flowing through the sensor. Looks like the plug itself may be bad....

 

[1990stanggt]

Does anyone else have anything I should check for? I'll be borrowing a multimeter from my dad this weekend to check out the sensor and plug......

 

[hotcobra03]

iat2

use a multimeter,,not a test lite......the volts are low and change with temps..you need a reference chart to compare volts to temps,,,,,


what is the reason for checking iat2? high intake temps?

 

[hotcobra03]

iat2

Intake Air Temperature Sensor
The intake air temperature (IAT) sensors (Figure 36) and integrated MAF type (Figure 39), are thermistor devices in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.

Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.

Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.

The IAT provides air temperature information to the PCM. The PCM uses the air temperature information as a correction factor in the calculation of fuel, spark and MAF.

The IAT sensor provides a quicker temperature change response time than the ECT or CHT sensor.

Supercharged vehicles use (2) IAT sensors. Both sensors are thermistor type devices and operate as described above. However, one is located before the supercharger at the air cleaner for standard OBD II/cold weather input, while a second sensor (IAT2) is located after the supercharger in the intake manifold. The IAT2 sensor located after the supercharger provides air temperature information to the PCM to control border-line spark and to help determine intercooler efficiency.

Currently two types of IAT2 sensors are used. A non-intergrated screw in type (Figure 36) and an integrated type, which is part of the Thermal Manifold Absolute Pressure (TMAP) sensor (Figure 43). The TMAP sensor consists of a IAT thermistor and a manifold absolute pressure (MAP) sensor. The thermistor portion of the TMAP is used for IAT2 function and operates in the same manner as a non-integrated IAT2. For additional information on the MAP portion of the TMAP, refer to the Thermal Manifold Absolute Pressure Sensor description and operation found later in this Section.



TEMPERATURE SENSOR VOLTAGE AND RESISTANCE SPECIFICATIONS Temperature Temperature Sensor Values
°C °F Voltage (volts) Resistance (K ohms)
120 248 0.27 1.18
110 230 0.35 1.55
100 212 0.46 2.07
90 194 0.60 2.80
80 176 0.78 3.84
70 158 1.02 5.37
60 140 1.33 7.70
50 122 1.70 10.97
40 104 2.13 16.15
30 86 2.60 24.27
20 68 3.07 37.30
10 50 3.51 58.75




2003 PCED OBD SECTION 5: Pinpoint Tests
Procedure revision date: 08/19/2002

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DU: Intake Air Temperature 2 (IAT2) DU: Introduction

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DU10 DTC P1115: SIMULATE OPPOSITE SIGNAL TO PCM
With IAT2 temperature sensor disconnected, connect a jumper wire between the sensor signal and SIG RTN circuits at the temperature sensor harness connector.
Key on.
Note: If a scan tool communication concern exists, remove jumper wire immediately and GO to DU12 .

Access IAT2 temperature sensor voltage PID.
Is the IAT2 temperature sensor voltage PID less than 0.2 volts?
Yes No
REPLACE suspect sensor. KEY OFF. REMOVE jumper wire. GO to DU11 .

DU11 CHECK TEMPERATURE SENSOR SIGNAL AND SIG RTN CIRCUITS FOR OPEN IN HARNESS
Note: Refer to the PCM connector pin numbers on this pinpoint test cover page.

Disconnect PCM.
Measure resistance of sensor signal circuit between PCM harness connector pin and IAT2 sensor harness connector.
Measure resistance of SIG RTN circuit between PCM harness connector pin and IAT2 temperature sensor harness connector.
Is each resistance less than 5.0 ohms?
Yes No
REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ). REPAIR open circuits.

DU12 CHECK TEMPERATURE SIGNAL FOR SHORT TO VREF IN HARNESS
Key off.
Disconnect PCM.
Measure resistance between IAT2 temperature signal circuit at the sensor harness connector and VREF circuits at the PCM harness connector.
Is the resistance greater than 10,000 ohms?
Yes No
REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ). REPAIR short to VREF.

DU20 P1114: SIMULATE OPPOSITE SIGNAL TO PCM
Disconnect harness from IAT2 temperature sensor.
Connect scan tool.
Key on.
Access IAT2 temperature sensor voltage PID.
Key off.
Is the IAT2 temperature sensor voltage PID greater than 4.2 volts?
Yes No
REPLACE sensor. GO to DU21 .

DU21 CHECK VREF VOLTAGE TO TP SENSOR
Refer to schematic at the beginning of the pinpoint test.
Disconnect TP sensor.
Key on, engine off.
Measure the voltage between VREF and SIG RTN circuits at the TP sensor harness connector.
Is voltage between 4.0 and 6.0 volts?
Yes No
There is sufficient VREF voltage. RECONNECT TP sensor. GO to DU22 . KEY OFF. GO to C1 .

DU22 CHECK TEMPERATURE SIGNAL CIRCUIT FOR SHORT TO GROUND IN HARNESS
Note: Refer to the PCM connector pin numbers on this pinpoint test cover page.

Disconnect PCM.
Measure resistance between sensor signal and SIG RTN circuits and then between sensor signal and PWR GND circuits at the PCM harness connector.
Is each resistance greater than 10,000 ohms?
Yes No
REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ). REPAIR short circuit.

DU30 P0127 IAT2 TOO HIGH. CHECK SUPERCHARGER INTERCOOLER PUMP OPERATION
Connect scan tool.
Access Output Test Mode.
Select Mode: ALL ON.
Command pump to run.
Does supercharger intercooler pump run?
Yes No
GO to DU31 . KEY OFF. GO to KP8 (Charge Air Cooler Pump).

DU31 CHECK INTERCOOLER SYSTEM
Check intercooler system for:
low fluid level.
cracked coolant lines.
blocked heat exchanger or coolant lines.
crossed coolant lines.
Is intercooler system OK?
Yes No
KEY OFF. GO to DU32 . REPAIR as necessary.

DU32 SIMULATE HIGH IAT2 VOLTAGE SIGNAL
Connect scan tool.
Key on.
Access IAT2 VPID.
Observe PID while disconnecting IAT2 sensor.
Is PID greater than 4.0V?
Yes No
GO to DU33 . REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ).

DU33 SIMULATE LOW IAT2 VOLTAGE SIGNAL
Access IAT2 VPID.
Observe PID while connecting a jumper wire between the sensor signal and SIG RTN circuit at the temperature sensor harness connector.
Is PID less than 1.0V?
Yes No
RECONNECT sensor and GO to Section 6 , Reference Values. COMPARE IAT2 PID to reference values under the given road test conditions. If sensor is not in range, REPLACE IAT2 sensor. REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ).




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[1990stanggt]

Thank you for all the info, I'll compare the readings I get to the chart. The reason I'm testing it is that when datalogging, the iat2 readings jump really fast, randomly between 0, 60, and 128. Changing the sensor, didn't change anything, I think the problem may be in the plug itself or the wiring, I'll be testing it tomorrow.