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Freeze Frame PID Definitions

Published on December 26th, 2023

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Purpose

To define the Freeze Frame PID terms, not all data in Freeze Frame is consistent.

What are PIDs?

OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J1979 defines many OBD-II PIDs. All on-road vehicles and trucks sold in North America are required to support a subset of these codes, primarily for state mandated emissions inspections. Manufacturers also define additional PIDs specific to their vehicles.

The freeze frame displays the PID or parameter ID values when the diagnostic trouble code (DTC) is triggered.

Freeze Frame PIDs

Tool DisplayUnitValuePID Description
 Fuel Sys 1 -OL Fuel System 1 Status
 Fuel Sys 2 -OL Fuel System 2 Status
 Calc Load % XXX.X Calculated LOAD Value
 ECT °C/ °F XXX/ XXX Engine Coolant Temp
 STFT B1 % XXX.X Short Term Fuel Trim-Bank 1
 LTFT B1 % XXX.X Long Term Fuel Trim-Bank 1
 MAP kPa/ PSI XXX/ XX.X Intake Manifold Absolute Pressure
 Eng RPM min XXXX Engine RPM
 Veh Speed kmm/h/mph XXX/XXX Vehicle Speed Sensor
 Spark Adv deg XX Ignition timing Advance #1 Cylinder
 IAT °C/ °F XXX/ XXX Intake Air Temperature
 MAF lb/min  XXXX.X/ XXXX.X Air Flow Rate from Mass Air Flow Sensor
 TPS % XXX.X Absolute Throttle Position
 O2S B1 S2 V X.XXX Oxygen Sensor Bank 1 - Sensor 2
 STFT B1 S2 % XXX.X Short Term Fuel Trim Bank 1 - Sensor 2
 Run Time sec
 Command EGR % XXX.X Commanded EGR
 Command EVAP % XXX.X Commanded Evaporative Purge
 Fuel Level % XXX.X Fuel Level Input
 Warm-up DTC Clr - XXX # Warm-ups since DTC Cleared
 Clr Dist miles
 EVAP_VP InH20
 BARO kPa/inHg XXX/XX.X Barometric

Fuel Sys 1 OL

The fuel injector in bank 1 is in an open-loop mode when the error occurred. In open loop mode, the engine doesn’t listen to anybody, it just runs off a set of instructions based on where the throttle is at, where the revs are, and so on. 

Fuel System 1 Status should be in closed-loop (CL). If the PCM is not able to achieve CL, the fuel trim data may not be accurate.

Fuel Sys 2 OL

The fuel injector in bank 2 is in an open-loop mode when the error occurred. Fuel System 2 Status should be in closed-loop (CL). If the PCM is not able to achieve CL, the fuel trim data may not be accurate.

Calc Load

Calculated LOAD Value indicates the normalized load value on the engine. It indicates a percentage of peak available torque. Reaches 100% at wide open throttle at any altitude or RPM for both naturally aspirated and boosted engines. 

ECT

This is the engine coolant temperature. Coolant displays engine coolant temperature (ECT) from a ECT sensor or cylinder head temperature sensor.

Engine Coolant Temperature (ECT) should reach operating temperature, preferably 190/F or higher. If the ECT is too low, the PCM may richen the fuel mixture to compensate for a (perceived) cold engine condition.

STFT B1

STFT B1 is Short Term Fuel Trim engine cylinder Bank 1. Short Term Fuel Trim (STFT) is what the engine computer is doing to the fuel mixture right now. This value changes rapidly and can bounce around quite a bit depending on engine load, speed, temperature and other operating conditions. Values normally range from negative 10 percent to positive 10 percent, though the readings may jump as much as 25 percent or more in either direction.

LTFT B1

LTFT B1 is Long Term Fuel Trim engine cylinder Bank 1. Long Term Fuel Trim (LTFT) is a longer term average of what the engine computer has been doing to balance the fuel mixture over a predetermined interval of time. This value is a more accurate indicator of how the fuel mixture is being corrected to compensate for changes in the air/fuel ratio that are occurring inside the engine.

MAP

This is the engine intake manifold pressure, and is measured by the MAP sensor. The PCM uses data from the MAP sensor to determine engine load, calculate fuel delivery, and (in some cases) calculate ignition timing and EGR operation. 

Eng RPM

RPM stands for Revolutions Per Minute. In a car, RPM measures the number of times the crankshaft spins in one minute. The spinning motion of the crankshaft, derived from the up-and-down motion of the engine’s pistons, translates to the spinning of the wheels which is what moves the car.

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Veh Speed

The vehicle speed sensor (VSS) measures transmission/transaxle output or wheel speed. The ECM uses this information to modify engine functions such as ignition timing, air/fuel ratio, transmission shift points, and to initiate diagnostic routines.

Spark Adv

Spark advance is the time before top dead center (TDC) when the spark is initiated. It is usually expressed in number of degrees of crankshaft rotation relative to TDC. 

IAT

The Intake Air Temperature sensor (IAT) monitors the temperature of the air entering the engine. The engine computer (PCM) needs this information to estimate air density so it can balance air air/fuel mixture. Colder air is more dense than hot air, so cold air requires more fuel to maintain the same air/fuel ratio. The PCM changes the air/fuel ratio by changing the length (on time) of the injector pulses.

MAF

The air mass information is necessary for the engine control unit (ECU) to balance and deliver the correct fuel mass to the engine. Air changes its density with temperature and pressure. In automotive applications, air density varies with the ambient temperature, altitude and the use of forced induction, which means that mass flow sensors are more appropriate than volumetric flow sensors for determining the quantity of intake air in each cylinder.

The Mass Airflow (MAF) Sensor, if the system includes one, measures the amount of air flowing into the engine. The PCM uses this information to calculate the amount of fuel that should be delivered, to achieve the desired air/fuel mixture. The MAF sensor should be checked for accuracy in various rpm ranges, including wide-open throttle (WOT), and compared with the manufacturer's recommendations. 

TPS

Absolute Throttle Position is the actual position of the throttle. A throttle position sensor (TPS) is used to monitor the air intake of an engine. The sensor is usually located on the butterfly spindle/shaft, so that it can directly monitor the position of the throttle. 

O2S B1 S2

O2 sensors are oxygen sensors. As the name implies, it senses the amount of oxygen that's in a mixture of gas or liquid, such as the exhaust that might come out of your car. 

Oxygen Sensor Output Voltage B1S1, B2S1, B1S2, etc., are used by the PCM to control fuel mixture. Another use for the oxygen sensors is to detect catalytic converter degradation. The scan tool can be used to check basic sensor operation.

STFT B1 S2

STFT B1S2 means Short Term Fuel Trim Bank 1 Sensor 2, which is the downstream 02 sensor from the catalytic converter. 

Run Time

Run time is the period from when the engine started running. This parameter may be useful in determining when a particular problem occurs during an engine run cycle.

Command EGR

The Exhaust Gas Recirculation or EGR system is one of several vehicle emission control systems. It helps reduce the amount of the nitrogen oxides (NOx) in the exhaust gases. Nitrogen oxides are normally formed in the process of combustion in the engine cylinders.

Commanded EGR is displayed as a percentage and is normalized for all EGR systems. EGR commanded OFF or Closed will display 0%, and EGR commanded to the fully open position will display 100%. Keep in mind this parameter does not reflect the quantity of EGR flow—only what the PCM is commanding.

Command EVAP

The Evaporative Emission Control System (EVAP) of a car contains a purge solenoid that is normally found between the intake manifold and containment canister that stores fuel vapor; both of which are in the vacuum line. When EVAP purge is commanded off, the value should be o%, and 100% when it is commanded on. This is an important parameter to check if the vehicle is having fuel trim problems. Fuel trim readings may be abnormal, due to normal purge operation. 

Fuel Level

The freeze frame can also show what was the fuel level in the tank is. Fuel Level Input indicates the nominal fuel tank liquid fill capacity as a percent of maximum. This is the percentage of fuel with 0% equaling tank is full and 100% when tank is empty.  Fuel level input is a very useful parameter when you’re attempting to complete system monitors and diagnose specific problems.

Warm-up DTC Clr

This parameter will count the number of warm-ups since the DTCs were cleared. A warm-up is defined as the ECT rising at least 40°F from engine starting temperature, then reaching a minimum temperature of 160°F. This parameter will be useful in verifying warm-up cycles, if you’re attempting to duplicate a specific code that requires at least two warm-up cycles for completion.

Clr Dist

Distance Since Cleared Diagnostic Codes is the distance driven since diagnostic trouble codes were erased.

EVAP_VP

Evaporative E missions System Vapor Pressure is pressure in the fuel tank.

BARO

Barometric Pressure is usually received from a dedicated barometer, manifold absolute pressure sensor, and other inputs during certain modes of driving. This parameter is useful for diagnosing issues with MAP and MAF sensors.

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