Powertrain Control Module Inputs

All of the sensors and input switches can be diagnosed by the use of a Tech 1. Following is a short description of how the sensors and switches can be diagnosed by the use of a Tech 1. The Tech 1 can also be used to compare the values for a normal running engine with the engine you are diagnosing.

ENGINE COOLANT TEMPERATURE (ECT) SENSOR
The Tech 1 displays engine coolant temperature in degrees Celsius and fahrenheit. After engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens. If the engine has not been run for several hours (overnight), the ECT and Intake Air Temperature (IAT) should be close to each other. A fault in the Engine Coolant Temperature (ECT) sensor circuit should set a Diagnostic Trouble Code (DTC) 14 or 15. The DTC charts also contain a chart to check for Engine Coolant Temperature (ECT) sensor resistance values relative to temperature.

KNOCK SENSOR
The Tech 1 will indicate when knock is present.

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The Tech 1 displays manifold absolute pressure and will display volts and kPa of pressure. Key "ON," engine stopped (no vacuum). MAP will display high voltage or pressure, while at idle (high vacuum), MAP will display low voltage or pressure. Likewise, on acceleration MAP will display high and on deceleration will display low voltage. A failure in the MAP sensor circuit should result in a DTC 33 or DTC 34.

MAF SENSOR
The Tech 1 displays grams per second. The PCM converts the Mass Air Flow (MAF) sensor input signal into grams per second, indicating the amount of air flow entering the engine. A failure in the MAF sensor circuit should result in a DTC 48.

INTAKE AIR TEMPERATURE (IAT) SENSOR
The Tech 1 displays temperature of the air entering the engine and should be close to ambient air temperature when engine is cold, and rise as underhood temperature increases. If the engine has not been run for several hours (overnight) the IAT sensor temperature and ECT sensors should display temperature readings close to each other. A failure in the IAT sensor circuit should set a DTC 23 or 25. The DTC charts also contain a chart to check for sensor resistance values relative to temperature.

HEATED OXYGEN SENSOR (HO2S)
The Tech 1 has several positions that will indicate the state of the exhaust gases. HO2S voltage, short term fuel trim. and long term fuel trim.
Normal Tech 1 voltage varies between 10 mV to 1000 mV (0.01 and 1.0 volt) while in "Closed Loop." DTC 13 and 63 will in one minute if voltage remains between 350 mV and 550 mV, but the system will go "open Loop" in about 15 seconds.

The PCM self-diagnostic circuit looks for trends in HO2S voltage. If a trend is detected, the Malfunction Indicator Lamp (MIL) (Service Engine Soon) comes "ON."

A rich exhaust trend causes the sensor voltage to stay above 700 mV for too long. This sets DTC 45 or DTC 65.

Lean exhaust causes voltage to stay below 300 mV for too long. This sets DTC 44 or 64. If voltage stays between 350 mV and 550 mV for too long, the PCM sets DTC 13 or 63. This indicates an open HO2S circuit.

Response Time
Not only is it necessary for the HO2S to produce a voltage signal for rich or lean exhaust, it is also important to respond quickly to changes. The PCM senses the response times. If the HO2S responds slowly, the customer may complain of poor fuel economy, rough idle or lack of performance. It may also set false PCM DTCs because the PCM uses oxygen sensor voltages for system checks.

HEATED OXYGEN SENSOR CONTAMINANTS
carbon
Black carbon or soot deposits result from over-rich mixtures. However, carbon does not harm a sensor. Deposits can be burned off in the engine by running it at least part throttle for two minutes.

Silica
Certain RTV silicone gasket materials give off vapors that contaminate the oxygen sensor. The sand-like particles from the RTV silica embed in the molecules of the sensor element and plug up the surface. This results in "lazy" HO2S response and engine control. The sensor will also have a white-like appearance.
There is also a possibility of silica contamination caused by silicone in the fuel. Careless fuel handling practices with the transport containers can result in unacceptable concentrations of silicone in the fuel at the pump.

There is also a possibility of silica contamination caused by silicon in lubricants used to install vacuum hoses on fittings.

Lead
Lead glazes sensors. It can be introduced when regular, or leaded fuel, is burned. It is difficult to detect lead contamination by visual inspection.

Other Substances
Oil deposits will ultimately prevent sensor operation. The sensor will have a dark brown appearance. Causes of high oil consumption should be checked.
The additives in ethylene glycol can also affect sensor performance. This produces a white-like appearance. If antifreeze enters the exhaust system, you will likely encounter other, more obvious symptoms of cooling system trouble.

Multiple Failures
If you encounter multiple or repeat HO2S failures on the same vehicle. consider contamination.
Leaded fuel, silica contamination from uncured, low-grade (unapproved) RTV sealant, and high oil consumption are possible.
A problem in the HO2S circuit or fuel system should set a DTC 13 or 63 (open circuit), DTC 44 or 64 (lean indication) or DTC 45 or 65 (rich indication). Refer to applicable chart if any of these DTCs were stored in memory.

THROTTLE POSITION (TP) SENSOR
The Tech 1 displays throttle position in volts and percentage of throttle blade opening, The value should display between about 0.3 - 0.9 volt, with throttle closed and ignition "ON," or at idle. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT) (about 4.6 volts).

The PCM has the ability to auto-zero the TP sensor voltage if it is between about 0.3 - 0.9 volt. This means that any voltage in this window will be determined by the PCM to be 0%) throttle. A failure in the TP sensor circuit should set a DTC 21 or 22. The Tech 1 has the ability to display the throttle angle and should be 0% when the throttle is closed.

A/C REQUEST SIGNAL
The Tech 1 should indicate A/C request as "YES," when A/C is requested.

PARK/NEUTRAL POSITION (PNP) SWITCH
The Tech 1 should display "P-N" when in park or neutral and "-R-DL" when in drive or reverse. Refer to CHART C-1A for PNP switch diagnosis.

REFERENCE SIGNAL
The Tech 1 will display this signal in RPM. Refer to Ignition System for more information on the distributor ignition system.

VEHICLE SPEED SENSOR (VSS)
The Tech 1 reading should closely match the speedometer reading with drive wheels turning. A failure in the VSS circuit should set a DTC 24 or 72.