Scan Tool Data Definitions Part 1

Introduction

The Scan Tool Data Definitions list contains a brief description of all of the engine related parameters that are available on the scan tool. The list is arranged in alphabetical order. A given parameter may appear in any one of the data lists, and in some cases the parameter may appear more than once, or in more than one data list in order to group certain related parameters together. The Transmission Scan Tool Data List is also covered under the Scan-Tool Diagnostics heading.

Data Definitions

A/C Load Signal - Scan tool displays: Heavy/Normal: This parameter will change state when the A/C compressor system is under an excessive load during, for example, any high air conditions. If the system pressure exceeds 1200 kPa, the ECM will detect this pressure via A/C load switch and increase the idle speed by about 50 RPM in order to compensate for the excess load.

A/C Compressor Control: Scan tool displays: A/C On/A/C Off: This display indicates that the ECM commands the A/C off when the engine temperature
exceeds a predetermined threshold, or a heavy acceleration maneuver has been initiated.

A/C Request - Scan tool displays: Yes/No: This parameter indicates that the A/C has been requested and therefore the idle air, as commanded by the
ECM, has been increased.

Actual MAF at Idle: Scan tool displays: 0.0 - 35.4 g/s: This parameter indicates the quantity of the air flowing into the engine during the idling conditions.

Avg. Inj. Pulse at Idle: Scan tool displays: 0.0 - 6.1 ms: This parameter indicates the average injector pulse width of both bank 1 and bank 2 injectors during the idling conditions.

Battery Voltage: Scan tool displays: 0.0 - 24.0 Volts: This parameter is the battery voltage at the ECM.

Calc. Converter Temperature: Scan tool displays: 0.0 - 1020.0°C: This parameter is a calculated catalyst temperature and is used for catalyst monitoring as well as disabling the HO2S heaters at temperatures exceeding 800°C in order to prevent damage.

Calculated Full Pos.: Scan tool displays: Active/Inactive: This parameter indicates that all full load maps are used (for example, the fuel enrichment and the ignition).

Calculated Idle Pos.: Scan tool displays: Active/Inactive: This parameter indicates that all idle maps are used (for example, the injection, the spark advance, and the idle air control).

Calculated Torque Reduction: Scan tool displays: 0 - 255 steps: This parameter represents the number of steps for the requested engine torque reduction (torque management).

Cam Signal Present: Scan tool displays: Low/High: This parameter indicates the presence of a CMP sensor signal. The value toggles Low to High with each transition of the CMP signal. Due to the refresh rate of the scan tool display, and the rapid changes in the signal state, this parameter may appear to freeze occasionally when the engine is running.

Compensation Gradient: Scan tool displays: 0.0 - 9.18 inches of H20: This parameter indicates the measured rise in the tank pressure when the [1][2]EVAP Purge valve and the EVAP Vent valve are closed.

Desired MAF at Idle: Scan tool displays: 0.0 - 35.4 g/s: This parameter indicates the calculated quantity of the air flowing into the engine during the idling conditions. The calculated quantity of air flowing into the engine is based on the engine load and the engine speed (RPM).

Desired Idle Speed: Scan tool displays: 0 - 2,550 RPM: This display shows the idle speed that is commanded by the ECM. The ECM will compensate for various engine loads in order to keep the engine close to the desired idle speed.

ECT: Scan tool displays: -48°C - 143°C: This display shows the temperature of the engine coolant.

ECT Sensor: Scan tool displays: 0.3-4.9 Volts: This parameter is the actual voltage on the ECT signal circuit as measured by the ECM.

Engine Load Signal: Scan tool displays: 0 - 12.75 ms: This is a calculated value that changes in proportion to the amount of the load on the engine.

Engine Speed: Scan tool displays: 0 - 10,200 RPM: This is essentially a digital tachometer display.

EVAP Canister Vent Valve: Scan tool displays: Active/Inactive: When the [1][2]EVAP diagnostic is executed, this parameter changes state from inactive to active, indicating that the EVAP Canister Vent Valve is closed.

[1][2]EVAP Leakage Factor: Scan tool displays: 0 - 1.992: This parameter indicates the level of the canister loading, and is used by the EVAP diagnostic to either enable or disable the on board test.

[1][2]EVAP Purge Valve: Scan tool displays: 0 - 100 percent: The ECM controls the EVAP Purge valve by using the Pulse Width Modulation (PWM). The display is the commanded pulse width (duty cycle) of the control circuit.

EVAP System Ready: Scan tool displays:No/Yes: This parameter indicates that the [1][2]EVAP diagnostic test has been performed at least once.

Fuel Level Output: Scan tool displays: 0 - 10.1 Volts: This parameter indicates the fuel level that is measured in volts in the fuel tank. Zero volts indicates near full while 10.1 volts indicates near empty.

Fuel Pump Relay: Scan tool displays: Off/On: The ECM enables the fuel pump when the CKP sensor pulses are detected.

Fuel Tank Pressure: Scan tool displays: -11.8 - 11.7 inches of H2O: This sensor is used in order to monitor the pressure within the EVAP system (which includes the fuel tank). The Fuel Tank Pressure sensor is very sensitive to changes in pressure. Inches of water is a very small unit of pressure measurement. One inch of H2O equals approximately 0.25 kPa.

Fuel Tank Pressure: Scan tool displays: O - 5 Volts: This parameter is the actual voltage on the Fuel Tank Pressure sensor signal circuit as measured by the ECM.

HO2S Bank 1 Sensor 1: Scan tool displays: -406 - 1,124 mV: This parameter is the actual voltage on the HO2S signal circuit as measured by the ECM.

HO2S Bank 1 Sensor 2: Scan tool displays: -406 - 1,124 mV: This parameter is the actual voltage on the HO2S signal circuit as measured by the ECM.

HO2S Bank 2 Sensor 1: Scan tool displays: -406 - 1,124 mV: This parameter is the actual voltage on the HO2S signal circuit as measured by the ECM.

HO2S Bank 2 Sensor 2: Scan tool displays: -406 - 1,124 mV: This parameter is the actual voltage on the HO2S signal circuit as measured by the ECM.

HO2S Bn 1 & Bn 2 Ready: Scan tool displays: No/Yes: This parameter indicates that the HO2S Bn 1 & Bn 2 diagnostic tests have been performed at least once.

HO2S Heaters Ready: Scan tool displays: No/Yes: This parameter indicates that the HO2S Heaters Bn 1 & Bn 2 diagnostic tests have been performed at least once.

HO2S Status Bank 1: Scan tool displays: Lean/Rich: When the HO2S voltage swings low, the Lean is indicated. The High signal voltage is indicated as Rich. When the sensor is active, this parameter will toggle rapidly. This parameter applies to the front (pre-catalyst) sensor.

HO2S Status Bank 2: Scan tool displays: Lean/Rich: When the HO2S voltage swings low, the Lean is indicated. The High signal voltage is indicated as Rich. When the sensor is active, this parameter will toggle rapidly. This parameter applies to the front (pre-catalyst) sensor.

IAC Long Term Air Trim: Scan tool displays: -100 - 100 percent: The ECM maintains the idle speed as close to the Desired Idle Speed as possible. Adjustments that are made by the ECM to compensate for the changes in the idle speed will be indicated by the Long and Short Term Air Trim values. The Short Term Air Trim values change rapidly in response to any minor fluctuations in the idle speed. These changes fine tune the idle RPM. The Long Term Air Trim values change in response to the trends in the Short Term Air Trim. The Long Term Air Trim makes coarse adjustments to the idle speed in order to re-center and restore control to the Short Term Air Trim. The Short and Long Term Air Trim can be monitored with a scan tool. The Ideal Air trim values are around 0 percent. A positive Air Trim value indicates that the ECM is adding Air (via the IAC valve) in order to compensate for a low idle speed condition. A negative Air Trim value indicates that the ECM is reducing the amount of Air in order to compensate for a high idle speed.

IAC Pulse Ratio - Scan tool displays: 0 - 65 percent: The ECM controls the IAC valve via two control circuits, one to drive the valve open and the other to drive the valve closed. The ECM Pulse Width Modulates both of the control circuits simultaneously. The ratio of the frequency between the two PWM signals determines the direction and the amount that the drive unit rotates the shutter within the valve.

IAC Short Term Air Trim: Scan tool displays: -100 - 100 percent: The ECM maintains the idle speed as close to the Desired Idle Speed as possible. The adjustments that are made by the ECM in order to compensate for changes in the idle speed will be indicated by the Long and Short Term Air Trim values. The Short Term Air Trim values change rapidly in response to the minor fluctuations in the idle speed. These changes fine tune the idle RPM. The Long Term Air Trim values change in response to the trends in the Short Term Air Trim. The Long Term Air Trim makes coarse adjustments to the idle speed in order to re-center and restore control to the Short Term Air Trim. The Short Term Air Trim and the Long Term Air Trim can be monitored with a scan tool. The ideal Air trim values are approximately 0 percent. A positive Air Trim value indicates that the ECM is adding Air (via the IAC valve) in order to compensate for a low idle speed condition. A negative Air Trim value indicates that the ECM is reducing the amount of Air in order to compensate for a high idle speed.

IAT: Scan tool displays: -48°C - 143°C: This display shows the temperature of the air entering the air induction system. The temperature should be close to ambient, however, high underhood temperatures and low vehicle speed may cause the IAT to climb.

IAT Sensor: Scan tool displays: 0.3 - 4.9 Volts: This voltage is the actual voltage on the IAT signal circuit to the ECM as measured by the ECM.