The short answer
Live data is the real-time readings from the sensors: temperature, revs, air flow, lambda sensors, battery voltage… Always start with engine temperature, fuel trims and voltage. Compare them with a car that runs well or with typical values, and use the graph to catch faults that last a second.
This is the function that separates people who clear faults from people who find them. You don't need to be an engineer: with five or six well-chosen parameters you can solve most engine problems.
How to get into live data
- Connect the tool and identify the car.
- Go into the control unit you are interested in (engine, gearbox, ABS…).
- Choose Live data.
- Select only the parameters you need. With 60 at once the screen crawls and you lose track. With 6 or 8 it refreshes quickly.
- Start the engine if the reading needs it and switch to the graph view to see how the values change.
- Record the session if you are doing a road test. That way you can go through it calmly afterwards.
The values worth checking first
These are a guide and vary from engine to engine. Use them as a reference, not a rule.
| Parameter | Typical value | What it tells you if it's out |
|---|---|---|
| Coolant temperature | About 85 to 105 °C when warm | If it won't rise above 70 °C, the thermostat is stuck open: higher consumption and mixture faults. Above 110 °C, there is a cooling problem. |
| Short-term and long-term fuel trim | Close to 0%, between -10% and +10% | Strongly positive: not enough fuel or unmetered air getting in (air leak, air flow meter, fuel pressure). Strongly negative: too much fuel (dripping injector, high pressure). |
| Upstream lambda sensor (narrowband) | Switches quickly between 0.1 and 0.9 V | Flat or slow: an ageing sensor or a mixture that is off. |
| Downstream lambda sensor | Steady, around 0.6 to 0.7 V | If it mirrors the upstream sensor, the cat is no longer working. Linked to P0420. |
| Battery voltage | 12.4 to 12.7 V engine off; 13.8 to 14.7 V running | Lower than that, look at the battery or alternator. Low voltage causes false faults in many control units. |
| Idle speed | Steady, not hunting up and down | If it hunts, look for air leaks, a dirty throttle body or misfires. |
| Misfires per cylinder | 0 or close to 0 | One cylinder with a high count points to that cylinder's plug, coil or injector. See P0300. |
On a diesel, also check
- Actual rail pressure against desired. If the actual figure falls short, suspect the filter, the pump or injectors with high back-leakage.
- Particulate filter differential pressure and its soot load. If it is high, see our guide to DPF regeneration.
- Actual and desired boost pressure, especially under load on a road test.
- Injector quantity corrections, on makes that show them. An injector well out of line with the others is often behind jerking and smoke.
Why use the graph
An intermittent fault lasts a second. You won't see it in a list of numbers; on the graph, you will. Put two parameters that should move together on the same screen (for example, throttle position and air flow) and look for the moment one breaks away from the other. Record the test and go through it with the car stopped.
Safety. If you are driving with the tool connected, have someone else hold it or leave it recording, securely fixed. Don't look at the screen while driving.
Which iCarsoft tools show live data
All of them, on the control units they cover. The difference is the screen and how comfortable it is to use. On a handheld tool such as the CR Pro the screen is smaller, so it is best to watch only a few parameters at a time. A tablet such as the CR Max P or the CR Ultra shows several graphs at once and records long sessions with ease, which you will appreciate when a diagnosis gets complicated. And if you want to activate components while watching the data (switching on the fan, moving the EGR valve), you need a bidirectional tool such as the CR Pro+.
