With flash codes, you are resorted to a standard procedure for dealing with problems which are relatively simple or just eliminating possibilities. Because once your car experience a malfunction that the engine doesn't sound as normal as it uses to be, you either know nothing about it or there are 2 many possible causes. That is when you turn the key on and the engine check light on the dash board is On, and doesn't turn off as the engine starts, you panic.
It's always best to have your own car's service manual, or not, insurance. Toyota is very open with car service manuals, so here we will test diagnostic with a 4A-FE 1999.
Procedure: Find the Diagnosis Plug(named on it), bridge E1 and TE1 using a piece of wire.
Ignition on, Engine OFF, Check engine light should flash frequently and will turn off when Engine is ON if there is no fault codes in the memory.
If there is any code, the light will flash accordingly: long pause-1st digit flashes-2nd digit flashes-long pause-repeat.
To make sure this system works correctly, we ask our tutor to create some faults, so then this will feel anonymous. When attempting to find the problem using diagnostic trouble codes(DTC), do a visual inspection after receiving the codes, after the faults were created, for example:
For the codes we get:
| Code Number | System Affected | Condition described |
| 41 | TPS | Throttle position sensor circuit |
| 22 | THW | Water temperature circuit |
| 31 | Vacuum sensor | Vacuum sensor circuit |
Loose connections in all 3 systems, all codes describe circuit problem, which is more likely to be connection problems=> So this is how we traced back to where exactly have gone wrong. Some time, the troubles are obvious that can be spotted by visual inspection. Sometime, electrical testing is carried out, only when we know where or the type of system involving - this is the kind of information the DTC is helpful about.
After repairing the fault, it is also important to clear the trouble codes, because it takes memory that we don't want into the system. Here is the procedure to clear the codes in DTC dignosis:
Turn off the engine
Switch Ignition Key off
Disconnect the battery
Wait 30seconds
Reconnect the battery and Ignition on
Check the Engine check light if it is flashing normally
Run the engine for the engine light to turn off
Make sure the codes are cleared.
Faults on any system of the Engine Management System will always affect engine's performance and efficiency, and safety one way or another. For example:
TPS unplugged: There is an Idle switch and a WOT switch, which will never be signaled to ECU, so at idle, ECU won't give out the best lambda mixture, or causes hesitation or lack of power when accelerating because ECU doesn't know where the throttle is exactly and the WOT switch is never on.
Scan tool Diagnostics
Unlike the DTC that differs from car to car, the Scan tool is the professional way to find faults in vehicle, in workshops, they are used by qualified auto electricians.
There are somethings to take note about this device: First, it is very expensive and it comes as a package to adapt on ANY model of modern vehicles. So when you try to find the ECU plug on your car you'd better find the right shape of adapter as well. Secondly, if you want to diagnose your car you must find the right brand, right model and the right year to start diagnose on the scan tool.
There are many features available on this specialized computer: Fault codes finding, Actuators testing, Live data sensors screen, which let you see the live data when the engine is running, coming from every sensor of the car, this is what it looks like:
With the live data feature, we can record the old normal data and compare it with the new data that the faults affect, and with the exact reading-by-sensor, you are pretty much sure about what is going on:
| Type of information(PID = Parameter Identification | Letters to describe it | Value of data (normal) | Value of data (faulty) | Units |
| Intake manifold | - | 14.6 | 31 | Kpa |
| ISC Duty | - | 10.09 | 7.7 | % |
| Output volume of FR | O2 sensor | 0.9 | 0.2 | V |
From here proceed with standard inspecting and repairing faults.
One more thing about the scan tool that is similar to the DTC system, that is clearing codes. One connected, the Scan tool displays the soul of the ECU, so they are pretty much in sync, therefore clearing codes is a must, and not hard, just few clicks away.
After clearing the codes, restart the scan tool and check for codes to make sure codes are cleared.
Clearly, the scan tool aid us from where to fix to reducing time of fault finding. Making it faster for simple problems and easier, more approachable for deeper, more sophisticated problems.
Good work Tung.
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sefa