For car enthusiasts and professionals alike, understanding the intricate workings of a vehicle’s engine is paramount. Modern vehicles are equipped with sophisticated On-Board Diagnostic (OBD2) systems that provide a wealth of data about engine performance. When you’re using an Autokraze Obd2 Scanner Review to assess your car’s health, two crucial parameters you’ll encounter are PID 04 (Calculated LOAD Value) and PID 43 (Absolute Load Value). These PIDs offer valuable insights into engine load, but deciphering what they truly mean can be complex. This article breaks down these parameters, making them understandable and useful for anyone using an OBD2 scanner.
Calculated LOAD Value (PID 04): Understanding Percentage of Peak Torque
The Calculated LOAD Value, represented by PID 04, is essentially an estimation of the percentage of peak engine torque currently being utilized. It’s not a direct measurement of torque, but rather a calculated figure that helps understand how hard the engine is working.
The formula for LOAD_PCT, as defined in OBD regulations, is designed to standardize this calculation across different manufacturers, improving accuracy. While manufacturers might have initially implemented this calculation in various ways, the standardized formula aims for consistency:
LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) * (BARO/29.92) * SQRT(298/(AAT+273))]Let’s break down the components:
- Current Airflow: This is the real-time measurement of air entering the engine.
- Peak Airflow at WOT@STP: This refers to the maximum airflow the engine can achieve at Wide Open Throttle (WOT) under Standard Temperature and Pressure (STP) conditions. This value is also a function of engine RPM.
- BARO: Barometric pressure. The formula adjusts for altitude by considering the current barometric pressure relative to standard sea level pressure (29.92 inches of Mercury).
- AAT: Ambient Air Temperature in Celsius. The formula also compensates for temperature variations, using 25°C (298K) as the standard temperature and adjusting based on the actual Ambient Air Temperature.
- SQRT: Square root.
Key Characteristics of LOAD_PCT (PID 04):
- Reaches 1.0 at WOT: Regardless of altitude, temperature, or engine RPM, the LOAD_PCT will reach 1.0 (or 100%) when the throttle is fully open. This makes it a useful normalized metric.
- Indicates Percent of Peak Torque: The value directly correlates with the percentage of the engine’s peak torque being used. A higher LOAD_PCT indicates the engine is working harder and producing more torque relative to its maximum capacity.
- Linearly Correlated with Engine Vacuum: As engine load increases, engine vacuum typically decreases, and vice versa. This correlation makes LOAD_PCT a good indicator of engine vacuum changes.
- Used for Power Enrichment: Engine control units (ECUs) often use LOAD_PCT to determine when to enrich the fuel mixture for optimal power, especially at higher loads.
- Diesel Engine Adaptation: Crucially, for diesel engines, the calculation adapts by using fuel flow instead of airflow. This allows diesel engines, which operate differently from gasoline engines, to also support and provide meaningful LOAD_PCT readings.
Absolute Load Value (PID 43): Air Mass per Intake Stroke
While Calculated LOAD Value (PID 04) provides a percentage-based estimate, Absolute Load Value (PID 43) offers a different perspective on engine load, focusing on the actual air mass entering the cylinders per intake stroke.
The formula for LOAD_ABS is defined as:
LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / intake stroke) * cylinder displacement in litres]And the derivation of air mass per intake stroke is:
air mass (g / intake stroke) = [total engine air mass (g/sec)] / [rpm (revs/min) * (1 min / 60 sec) * (1/2 * # of cylinders (strokes / rev))]Let’s unpack this:
- Air mass (g / intake stroke): This is the core of the PID. It represents the mass of air, in grams, that is drawn into each cylinder during each intake stroke. It’s calculated from the total engine air mass flow rate and engine speed (RPM), considering the engine’s four-stroke cycle.
- Cylinder Displacement: This is the engine’s swept volume in liters.
- 1.184 (g / litre): This constant represents the density of air at STP (Standard Temperature and Pressure). It’s used to normalize the air mass per intake stroke against the engine’s displacement.
Key Characteristics of LOAD_ABS (PID 43):
- Ranges: For naturally aspirated engines, LOAD_ABS typically ranges from 0 to around 0.95. For turbocharged or supercharged (boosted) engines, it can go significantly higher, from 0 to 4 or even more. This difference highlights how boosted engines can significantly exceed the air intake of naturally aspirated engines.
- Linearly Correlated with Torque: LOAD_ABS shows a linear correlation with both indicated torque (torque produced inside the cylinders) and brake torque (torque available at the crankshaft). This makes it a very direct indicator of engine torque output.
- Used for Engine Control Strategies: ECUs utilize LOAD_ABS for scheduling spark timing and Exhaust Gas Recirculation (EGR) rates, optimizing engine performance and emissions based on the actual air intake.
- Correlates with Volumetric Efficiency: The peak value of LOAD_ABS at WOT is directly related to the engine’s volumetric efficiency – how effectively the engine fills its cylinders with air.
- Indicates Pumping Efficiency: LOAD_ABS can be used diagnostically to assess the engine’s pumping efficiency, revealing potential issues that might restrict airflow.
- Spark Ignition Engine Requirement: Importantly, PID 43 (Absolute Load Value) is required for spark ignition (gasoline) engines. While it’s not mandatory for compression ignition (diesel) engines, some diesel vehicles might still support it.
Why Understanding PID 04 and PID 43 Matters for Autokraze OBD2 Scanner Review Users
When you are conducting an Autokraze OBD2 scanner review or using an OBD2 scanner for vehicle diagnostics, understanding PID 04 and PID 43 can significantly enhance your analysis.
- Engine Performance Assessment: By monitoring these PIDs, you can get a real-time view of how hard your engine is working under different driving conditions. High load values can indicate demanding situations like uphill driving, acceleration, or towing.
- Identifying Potential Issues: Unusually high or low load values, or discrepancies between expected and actual load readings, can point to potential engine problems. For instance, a consistently high LOAD_ABS at idle might suggest vacuum leaks or other issues.
- Comparing Engine Types: Understanding the differences between PID 04 and PID 43, and how they are calculated for both gasoline and diesel engines, is crucial for accurate interpretation, especially when working with different vehicle types using your Autokraze OBD2 scanner review.
- Informed Vehicle Maintenance: Armed with the knowledge of engine load parameters, you can make more informed decisions about vehicle maintenance and driving habits to optimize engine health and fuel efficiency.
In conclusion, while Autokraze OBD2 scanner review often focuses on ease of use and features, understanding the data provided by these scanners, particularly PIDs like 04 and 43, unlocks a deeper level of vehicle diagnostics and performance analysis. By grasping the nuances of Calculated LOAD Value and Absolute Load Value, you can move beyond simply reading codes and truly understand what’s happening under the hood of your car.
