As an auto repair professional, you’re likely familiar with Calculated Load Value in OBD2 data. It’s a standard Parameter ID (PID) that provides insight into engine load. However, have you ever considered Absolute Load Value Obd2? This PID, while perhaps less commonly used in day-to-day diagnostics, offers a potentially deeper understanding of engine performance, particularly concerning engine breathing and efficiency.
Recently, a discussion on ScannerDanner forum highlighted this very point, showcasing a data capture from a Mazda 3. This sparked a crucial question: Is Absolute Load a more valuable diagnostic tool than Calculated Load, or are there scenarios where using both provides a distinct advantage? Let’s delve into the details to understand the nuances of Absolute Load Value.
To understand the difference, referencing an SAE document is beneficial. According to SAE specifications, both Calculated Load (LOAD_PCT) and Absolute Load (LOAD_ABS) offer unique perspectives on engine operation.
Characteristics of LOAD_PCT are:
Reaches 1.0 at WOT at any altitude, temperature or rpm for both naturally aspirated and boosted engines. Indicates percent of peak available torque. Linearly correlated with engine vacuum Often used to schedule power enrichment. Compression ignition engines (diesels) shall support this PID using fuel flow in place of airflow for the above calculations.
Characteristics of LOAD_ABS are:
Ranges from 0 to approximately 0.95 for naturally aspirated engines, 0 – 4 for boosted engines, Linearly correlated with engine indicated and brake torque, Often used to schedule spark and EGR rates, Peak value of LOAD_ABS correlates with volumetric efficiency at WOT., Indicates the pumping efficiency of the engine for diagnostic purposes.
OBD2 data capture from a Mazda 3 showcasing Absolute Load Value and Calculated Load Value at idle
The key takeaways here are the distinctions in what each PID represents. Calculated Load is designed to reach 1.0 at Wide Open Throttle (WOT) regardless of conditions, essentially indicating the percentage of peak available torque. Absolute Load, on the other hand, ranges differently for naturally aspirated and boosted engines and is directly linked to both indicated and brake torque.
Crucially, Absolute Load is highlighted as an indicator of pumping efficiency and its peak value correlates with volumetric efficiency at WOT. This is where its diagnostic potential becomes particularly interesting for auto repair experts. Engine breathing problems, such as intake restrictions, directly impact pumping and volumetric efficiency.
So, should you be prioritizing Absolute Load Value OBD2 in your diagnostic routine? While Calculated Load remains a useful general indicator, Absolute Load offers a more direct window into engine efficiency. By monitoring Absolute Load, you can gain insights into potential issues affecting engine breathing, which might be less obvious when solely relying on Calculated Load.
For a comprehensive diagnostic approach, utilizing both PIDs could be advantageous. Comparing Calculated Load and Absolute Load values under various engine conditions, especially during WOT and under suspected engine breathing restrictions, can provide a more complete picture of engine performance.
Further real-world data and testing are always beneficial. Observing how both PIDs respond under known good conditions and when introducing engine breathing faults would solidify our understanding and application of Absolute Load Value OBD2 in automotive diagnostics. Exploring Absolute Load Value PID is a worthwhile endeavor for any auto repair professional looking to enhance their diagnostic toolkit and gain a deeper understanding of engine performance metrics.
