How to read OBD live data: Step-by-step guide

How to read OBD live data: Step-by-step guide
Ever had a car hiccup that wouldn't show up as a fault code? Not every irregularity or noise from your vehicle triggers an immediate fault code. Sometimes, car issues need to occur multiple times before the system detects them. 
Welcome to the realm of OBD live data – your automotive detective. With live data, you can catch potential problems in real time. Often before they become major concerns. 
This guide will help you understand the purpose of live data and how to use it to master car diagnostics. 

What is OBD live data? 

The OBD live data is real-time details your car's sensors and systems keep sending out when your engine is running. While fault codes tell you "what" is wrong with your car, live data unravels the "why," "where," and the "how." Simply put, it provides much more detailed information about the issue. 
With live data, you can monitor a wide range of parameters like engine revolutions (RPM), engine load, manifold pressure, coolant temperature, fuel system status, vehicle speed, and more. 
By interpreting these live sensor data, you can address issues beforehand. This leads to better fuel efficiency and enhanced engine performance. It may even extend the life of components like the catalytic converter and EGR valve
Plus, the live data feature is handy tool to find out the real causes of trouble codes. It becomes particularly helpful when the check engine light appears on your dashboard. 

Basic OBD2 live data values 

Name Description Optimal value (may vary between different cars)
Short Term Fuel Trim The short term fuel trim in percentage Between -5% to +5%
Long Term Fuel Trim The long term fuel trim in percentage Between -5% to +5%
Engine Coolant Temperature The temperature of the engine’s coolant in degrees Celsius Between 70-105 °C
Engine Oil Temperature The temperature of the engine oil in degrees Celsius Between 70-105 °C
Intake Manifold Absolute Pressure The pressure in the intake manifold in kilopascals Varies by engine and load
Ignition Timing The ignition timing in degrees 5-20°
Calculated Engine Load The engine load in percentage Varies by driving conditions
Mass Air Flow The amount of air entering the engine in grams per second Varies by engine and load
Engine Speed (RPM) The number of times the engine’s crankshaft rotates per minute 600-900 RPM at idle if the engine is heated up
Intake Air Temperature The temperature of the air entering the engine in degrees Celsius Varies by engine and load
Charge Air Temperature The temperature of the air entering the engine after being compressed by the turbocharger or supercharger in degrees Celsius Varies by engine and turbocharger/supercharger
Throttle Position The position of the throttle in percentage Between 0-100%
Oxygen Sensor Bank 1 Sensor 1 The voltage output of the oxygen sensor in millivolts for Bank 1 Sensor 1 Between 0.1-0.9V for a properly functioning sensor
Oxygen Sensor Bank 1 Sensor 2 The voltage output of the oxygen sensor in millivolts for Bank 1 Sensor 2 Between 0.1-0.9V for a properly functioning sensor
Catalyst Temperature The temperature of the catalytic converter in degrees Celsius Between 200-800 °C
Exhaust Gas Recirculation The percentage of exhaust gases being recirculated into the engine Varies by engine and load
Alternator Voltage The voltage output of the vehicle’s alternator in volts Between 13.5-14.5V
Battery Voltage The voltage of the vehicle’s battery in volts Between 12.4-12.8V with the engine off
Open/Closed Loop Indicates if the fuel system is operating in a closed or open loop Closed loop

Vehicle systems you should keep an eye on 

To make the most of the OBD2 live data, it's crucial to focus on key areas of your car. Here are the main control units and their parameters worth monitoring to ensure your car's longevity: 
Your car's engine isn't just the heart of the vehicle – it's also one of the most expensive parts to fix. Monitoring these parameters can save you from unexpected expenses down the road: 
  • Throttle position 
  • Engine load 
  • Air and fuel mixture 
  • Engine coolant and oil temperature 
  • Manifold Absolute Pressure (MAP sensor) 
  • Intake air temperature 
  • Short term fuel trim and long term fuel trim 
  • Ignition timing 
  • Oxygen sensor voltage 
These readings are vital for understanding your vehicle's engine health. They can help you spot things like vacuum leaks or the need to adjust fuel pressure. 
For cars with automatic transmissions, monitoring the gearbox is key to smooth driving. Keep an eye on these parameters to know how your transmission is doing: 
  • Transmission fluid temperature 
  • Current gear 
  • Torque converter hydraulic pressure 
  • Torque converter clutch slipping 
Tracking these live data readings from the transmission can help you prevent gear shifting or overheating problems. 
Think of your braking system as your car's lifeline, quite literally. It doesn't only affect the car's ability to stop –it's keeping you alive and safe. Live data values can help identify: 
  • ABS systems condition 
  • Brake pressure 
  • Vacuum brake booster condition 
  • Traction control system parameters 
  • Status of Electronic Differential Lock 
The live data in the brakes control unit allows you to monitor not only the performance of the brakes but also other important safety systems, such as ABS (Anti-Lock Braking System), ESP (Electronic Stability Program), or even traction control. 
Other systems 
Some diagnostic apps like OBDeleven VAG gather live data from even more vehicle systems. You can also read manufacturer-specific data like: 
  • Multimedia system run time 
  • HVAC (heating, ventilation, and air conditioning) system data, such as external and internal temperature, position of flaps 
  • Calibration values 
By understanding live data values, you can enjoy an unparalleled diagnostic experience. This not only helps to find the roots of issues. It gives you a better understanding of the car and how it functions. 
 A person holding a smartphone inside a car, with an OBDeleven OBD2 scanner app open displaying live sensor data, including a chart of the calculated engine load and its numerical value from the engine control module.

Practical tips for using Live Data in OBDeleven 

Just like we said – with the OBDeleven VAG app, you can access all possible OBD2 and manufacturer-specific live data parameters. 
Accessing live data in this app is relatively easy. Firstly, find the OBD2 port and plug in the OBDeleven NextGen or FirstGen device. Then, establish a Bluetooth connection with the app, navigate to the control units section, select the relevant unit, and tap "Live Data."  
Accessing the live data feature in the OBDeleven app is even more straightforward. Plug in the device, connect, open the "Vehicle" screen, and select "Live Data." 
Although our other app – OBDeleven – for non-Toyota and non-BMW group vehicle owners doesn't offer as wide a list of parameters as for VAG group vehicles, it still contains the most important and commonly checked live data values: 
  • Calculated engine load 
  • Engine coolant temperature 
  • Intake Manifold Absolute Pressure (MAP) sensor 
  • Engine speed (RPM) 
  • Mass Air Flow (MAF) sensor 
Now, let's see how you can use live data to diagnose and troubleshoot your car: 
Short/long term fuel trim 
Fuel trim is key to detecting whether your car is running lean (less fuel) or rich (more fuel) than ideal. It's about how your car's system manages fuel. You can check this via a diagnostic scan tool tool by looking at Short-Term Fuel Trim (STFT) and Long-Term Fuel Trim (LTFT). These values are usually displayed as percentages. 
Ideal STFT and LTFT readings hover around -5% to 5%. Readings significantly higher or lower can indicate a problem. 
High readings may suggest a lean fuel mixture, often checked by ensuring the gas cap is secure. Other causes can be vacuum leak or faulty sensors, like O2 sensors (also known as Oxygen or Lambda sensor), signaled by specific fault codes. 
Negative fuel trim readings can point to a rich fuel mix. This issue can potentially be caused by problems with sensors such as MAP or O2 sensors. It can also be caused by leaking fuel injectors.  
It's often easier to notice these problems when the engine warms up. You can also identify them through fault codes. 
Engine coolant temperature 
For your vehicle to run efficiently, the engine's coolant temperature should ideally be between 70°C and 105°C (160-220°F.) Exceeding this range hints at potential troubles in the cooling system. These troubles often occur due to low or aged coolant, which can be resolved with a refill or a complete flush. 
Addressing high coolant temperatures is essential to prevent significant engine damage. 
The engine coolant temperature sensor plays a crucial role in indicating the engine's heat level. Which affects the air-fuel mixture. Engines need a richer mix when cold and a leaner mix when warm. 
A malfunctioning sensor may inaccurately indicate that the engine is cold when it's overheating. To check the sensor's accuracy, compare its readings with the temperature measured by a thermometer. 
Additionally, if the engine struggles to reach the optimal temperature or overheats rapidly, it could signal an issue with the thermostat being stuck. This condition disrupts the engine's ability to regulate its temperature. It requires prompt attention to avoid further complications. 
 A close-up view of a car engine bay, showing a coolant reservoir, various hoses, electrical wiring, and a portion of the air intake system.
Engine oil temperature 
Monitoring the engine oil temperature is vital, particularly for drivers who enjoy a more spirited driving style. Pushing an engine hard before it reaches its proper oil operating temperature is risky. 
Top-notch engine oils are designed to withstand temperatures up to about 120°C (250°F) before their quality starts to deteriorate. 
Typically, once your vehicle warms up, the oil temperature will be slightly higher than the coolant temperature. 
Transmission oil temperature 
Monitoring the transmission oil temperature may prevent costly repairs for vehicles with automatic transmissions. Ideally, it should remain between 80°C to 105°C (175-220°F). Exceeding this range by 10°C (20°F) or more signals potential transmission issues. 
It's important to keep an eye on these temperatures to ensure the transmission operates efficiently and avoids costly damage. 
Intake manifold absolute pressure 
Monitoring the Manifold Absolute Pressure (MAP) sensor data is key for your vehicle's engine to run smoothly. This sensor helps the engine's control unit adjust fuel delivery and timing. 
Normal MAP readings change based on your car's needs. These changes occur especially when accelerating or driving under different conditions. If the MAP readings are higher or lower than usual, it might point to some common problems. 
Unusual readings can indicate potential problems. High values might suggest intake system blockages or vacuum leaks. While low values could point to sensor malfunctions or leaks in the intake manifold. 
Keeping an eye on MAP sensor inputs is a good way to ensure your engine works efficiently and to spot issues early. Changes in these readings might affect how well your engine performs and how much fuel it uses. They can also cause the check engine light to turn on. 
Understanding these sensor readings can help you take care of your car's engine and avoid more serious problems in the future. 
Ignition timing 
The timing of ignition directly affects the engine's health and performance. Incorrect timing, whether too early or too late, can lead to engine vibrations. This can cause potential damage, impacting the engine's longevity, power, and fuel efficiency. 
When your car's engine detects a fuel mixture that's too rich, or you press the accelerator, it adjusts the ignition timing to occur earlier. This helps prevent the engine from getting flooded with fuel, a process known as ignition advancing. 
Conversely, if the fuel mixture is too lean, the engine will slightly delay the ignition. This delay, known as ignition retarding, allows more fuel to enter the combustion chamber, balancing the air-fuel mixture. 
You can check this through the "Ignition timing advance" reading. A positive number in this reading indicates that the ignition is being advanced. While a negative number means it's being retarded. Normally, the spark advance should be within a range of 5 to 20 degrees when your car is idling. 
If you notice irregular ignition timing, it could hint at underlying issues with critical engine components like pistons or valves. 
Calculated engine load 
This parameter provides a snapshot of your engine's current load compared to its maximum potential. Monitoring this helps in assessing whether the engine is overworked or underutilized. It's a helpful aspect to maintain engine health and optimize fuel consumption. 
Mass Air Flow (MAF) sensor 
This sensor's data determines the amount of air entering the engine, which impacts the air-fuel mixture. Incorrect readings can have a negative impact on your vehicle's performance. This includes reduced fuel efficiency and increased emissions. 
Engine speed (RPM) 
Engine speed, commonly referred to as RPM (revolutions per minute), is a fundamental measure of how fast your engine is running. This measurement is crucial for controlling key functions such as ensuring proper timing for fuel injection and ignition. 
The RPM helps manage shifting points in cars with automatic transmissions, providing a smoother driving experience. 
While a scan tool is not necessary to view these RPM readings – as they're typically visible on your car's dashboard – they're important to observe. Keeping an eye on RPM is vital because it helps you understand how various engine parameters shift in response to changes in engine speed.
A person is holding a smartphone displaying an OBDeleven OBD2 scanner app with live sensor data from a vehicle. Visible readings include oxygen sensor data, coolant temperature, engine speed, vehicle speed sensor data, and ignition timing adjustment data.

What's next 

Diving deeper into OBD2 live data is just the beginning. With the OBDeleven, you can go far beyond just that. 
Explore the possibilities of this powerful tool and join a community of car enthusiasts. 
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