If you are just a general car owner or starting hobby mechanic, you might feel confused after looking at the engine live data on your freshly purchased OBD2 scanner.
I will briefly explain the basic live data to help you understand what you are looking at.
Engine live data explained!
Let’s break down engine live data from your OBD-II scanner. This info helps you understand what’s happening with your car’s engine. We’ll focus on the engine-related data and what you can infer from it.
What is a Bank in OBD2?
In OBD2, “Bank” refers to engine heads. A 4-cylinder engine has one head (Bank 1), while V-shaped engines have two heads (Bank 1 and Bank 2). For example, LTFT1 is the long-term fuel trim for Bank 1, and STFT2 is the short-term fuel trim for Bank 2.
Fuel System Status (OL/CL)
The fuel system can operate in open-loop (OL) or closed-loop (CL) mode. Open-loop uses preset fuel maps and ignores the O2 sensor. Closed-loop adjusts fuel delivery using O2 sensor feedback for an optimal air/fuel ratio (14.7:1), improving efficiency and reducing emissions.
Engine Coolant Temperature (ECT)
The optimal temperature range is 194-219°F (90-104°C). This helps indicate if the engine is running within the proper temperature range, preventing overheating or inefficient operation.
Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT)
STFT shows real-time fuel adjustments. High values can indicate issues like vacuum leaks. LTFT shows long-term adjustments. High values may point to problems with the O2 sensor or catalytic converter. Ideally, these values should be under ±5%. Fuel trims are most important data and you can understand them better in this complete guide.
Revolutions Per Minute (RPM)
The idle range is typically 600-900 RPM. If idle RPM is higher than 1000, it could indicate problems or specific engine operations like DPF regeneration or cold engine start.
Intake Air Temperature (IAT)
IAT measures the temperature of air entering the engine. The ECM uses this data to adjust the air/fuel mix and ignition timing, affecting performance and efficiency.
Throttle Position
The throttle position is expressed as a percentage (0% = closed, 100% = fully open). It helps the ECM determine the correct fuel delivery and ignition timing for optimal performance.
Oxygen Sensor Output (O2)
O2 sensors monitor exhaust gases to adjust the air/fuel mix. The optimal voltage should fluctuate between 0.1 and 0.9V, indicating proper sensor function and fuel mix.
Mass Airflow Sensor (MAF)
MAF measures air entering the engine in grams per second (g/s). This data helps the ECM adjust the air/fuel ratio, which is crucial for engine performance and emissions control.
Catalyst Temperature
The catalytic converter needs to be around 400-600°C (750-1100°F) to function properly. This temperature ensures it effectively reduces emissions.
Engine Gas Recirculation (EGR)
EGR data includes valve position, flow rate, and temperature. It ensures the EGR system is working correctly to reduce nitrogen oxide emissions and improve efficiency.
Alternator Voltage
The optimal range is 13.5-14.5V. Consistently lower or higher values indicate potential issues with the alternator or charging system, which can affect battery life and electrical system performance.
Battery Voltage
A fully charged battery should read 12.6-12.8V when the engine is off and 13.5-14.5V when running. Deviations can indicate battery or charging system problems.
Engine Oil Temperature
The optimal oil temperature range is 195-220°F (90-105°C). Maintaining this range ensures the engine operates efficiently and avoids damage due to overheating.
Malfunction Indicator Light (MIL)
A lit MIL indicates potential issues with the vehicle. Addressing these issues promptly can prevent further damage and maintain performance and efficiency.
Manifold Absolute Pressure (MAP)
MAP measures pressure in the intake manifold. Optimal idle readings are 28-32 kPa, while wide-open throttle should be 250-300 kPa. Deviations can indicate engine or sensor issues.
Vehicle Speed (VSS)
VSS monitors the car’s speed and is labeled variously as SPD, MPH, KPH, etc. It helps the ECM manage fuel delivery and transmission shifting.
Charge Air Temperature (CACT)
The optimal CACT is below 140°F (60°C). Higher readings can indicate issues with the turbocharger or intercooler, affecting performance and fuel efficiency.
I also explain these data in more detail in my eBook:
Diagnostics Introduction!
- Automotive electrical basics
- OBD-II scanner basics
- Using cheap tools to diagnose faults
- Bi-directional scan tool introduction
- OBD-II scanner Buyer’s Guide
- Free diagnostics training
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko
thank you for good information
No problem, I am happy its helpful.
Thanks for the explanations. For a music project I am working on I want to read Vehicle speed, RPM and throttle in realtime and send that data to my application (running on Mac OS). What scanner do you suggest for that? Thanks
You can do that with Veepeak + Car Scanner app and then export data to your computer
hello sir, thanks for the great information. but i have a 2014 mirage with no engine codes but it consumes twice the recommended fuel. the upstream oxygen sensor reads from 2v-4v with all scanners i have used. is that possible or its always between 0.1 and 0.9v. also i smell gas in the exhaust fumes when i spark, until iit warms up.
hello
in Manifold Absolute Pressure (MAP) part you said: “… while wide-open throttle should be 250-300 kPa.”
It seems that this number is wrong. Because the sea level pressure is about 101kpa. My car shows 89 in this mode at an altitude of 900 meters.
Of course, I know that the situation is different for turbocharged cars.
I have a question that I couldn’t find the answer to no matter what I searched on the internet. In the diagnostic devices used by mechanics, the amount of injector fuel injection is shown in each cycle. Is there a dongle and software that will give me this number?