How to Read Engine Codes without a Reader – A Simple 4-step Method

For both OBDI and OBDII vehicles, when the CEL/MIL ( Check Engine Light/Malfunction indicator light) lights up on the dashboard after the vehicle starts. This is a simple way the vehicle tells you something is wrong with its health. Failure to pay attention to this notice could lead to a total breakdown of the vehicle, leading to a more expensive repair. Due to this reason, Knowing how to read engine codes without a scanner could be helpful.

Many car owners have been through a scenario where the CEL/MIL refuses to turn off after the vehicle starts. And they spend more money on trying to get the different fault codes. They do it either by buying a scan tool (Code reader) or taking the car to mechanics/dealerships to get the scanned codes (Engine codes) present with the vehicle. This could be more expensive than the actual repair to be carried out on the vehicle.

Sometimes, the CEL/MIL could illuminate because you forgot to tighten the Gas Cap properly, but how would you know this was the issue if the only information you had was just the CEL/MIL? This is why you need to know how to read engine code reader,

In this article, you will learn how to read engine codes without a code reader.

how to check engine codes

Reading engine codes without a reader in 4 Steps

First, you need to identify if your vehicle is an OBDI or an OBDII Vehicle to decipher the Engine codes from your vehicle. 

If you need help to know whether your vehicle is an OBDI or an OBDII, note that the vehicles from 1996 to date are OBII vehicles, and vehicles produced from 1995 downward are OBDI. But some models started equipping their vehicles with OBDII as early as 1994. If you are still trying to figure out if you have an OBDII or OBDI vehicle, don’t worry; follow the steps to learn how to read engine codes without a reader below and pay close attention to all lights on the dashboard/instrumental cluster.

Step 1

  1. Insert your key into the ignition;
  2. Turn the ignition to the on position and do not crank the engine;
  3. Inspect all lights on the dashboard; the following should illuminate:- CEL/MIL, Battery Light, odometer reading, etc.
  4. Check if the CEL/MIL illuminates; if it does not illuminate, try starting your vehicle. If the vehicle starts without the CEL/MIL illuminating, the CEL/MIL Bulb is blown;
  5. You can only proceed with this procedure if fixing the issues with the CEL/MIL Bulb if your vehicle is an OBDI.

Note:- For all OBDI vehicles, the CEL/MIL must illuminate during the dashboard lights check 

Step 2

  1. After verifying the dashboard lights are responsive, turn the ignition to the off position and remove the key;
  2. Insert your key back into the ignition;
  3. Turn the ignition to the on position and back to the off position quickly. Repeat this procedure 3 times but do not crank the engine during the process;
  4. If you mistakenly crank the engine during the quick key cycling procedure, you will need to re-start the procedure from Step2(1);
  5. After you successfully cycle the key quickly up to 3 times by Turning the ignition to the on and off position, at the 3rd cycle, pay attention to the dashboard/instrumental cluster; 
  6. If your vehicle is OBDI, continue with the information in ( Step 3);
  7. If your vehicle is OBDI, continue with the information in ( Step 4).

Step 3

  1. On the dashboard, pay attention to the flashing CEL/MIL;
  2. Every code starts with a slow flashing light, then a pause followed by a fast blinking light;
  3. All OBDI codes are two digits, so you need to take note of the amount of time the CEL flashes slowly and the amount of time it flashes quickly;
  4. The amount of time it flashes slowly represents the first digit of every code, while the fast flash represents the second digits
  5. If the CEL/MIL flashes once, it represents digit 1; if it flashes twice, it represents digit 2. But if it flashes 10 times, it represents the digit 0.

Example of OBDI codes:-

  1. A) CEL/MIL flashes slowly 2 times, pauses a bit, and starts flashing fast 10 times. OBDI Code interpretation: code- 20
  2. B) CEL/MIL flashed slowly 2 times, then it paused a bit and started flashing fast for 10 times, then paused again, then started flashing slowly 5 times, then paused a bit and started flashing 9 times.

OBDI interpretation:

Code:- 20

Code:- 59

  1. C) CEL/MIL flashed slowly 2 times, then it paused a bit and started flashing fast for 10 times, it paused again, then started flashing slowly 2 times, it paused a bit and started flashing quickly 10 times paused and flashed quickly again 1 time.

OBDI interpretation:

Code:- 20

Code:- 201

  1. D) CEL/MIL flashed slowly 2 times, paused, and flashed again slowly 2 times.

OBDI interpretation:-

Code:- 2

Code:- 2

6) After you get the codes, check your user manual for code interpretation or research what the codes mean for your vehicle model.

Step 4

  1. On the dashboard/instrumental cluster, pay attention to the odometer reading display. 
  2. Immediately after the 3rd attempt of cycling the key on and off, the scanned codes will display on the odometer display screen
  3. Take note of all codes and do your research on the interpretation of the code 
  4. If no codes are present, the odometer will display either done or completed, but for some vehicles, it will just display dashes, then re-display the odometer value.

Other than following the steps above, it is possible to use the odometer trip button to learn how to check engine codes without a reader, even though it does not work for all models.

I will not advise this step since you might mistakenly reset your trip during the process, which might not be your intention.

how to read check engine codes

Frequently Asked Questions-FAQs

Q: Can you read the engine code without check engine light?

No, if your Engine light bulb is blown or won’t just illuminate. It is impossible to read the fault code on an OBD1 vehicle without a scanner. But for an OBDII vehicle, yes, you can read the fault codes without a scanner if your odometer display works perfectly.

Q: What is the most common check engine code?

The common engine codes are:

  • Transmission code:- P0700 Transmission Control System Malfunction;
  • Misfire code: P0300 Random or Multiple Cylinder Misfire Detected;
  • Oxygen sensor codes: P0155 – HO2S B2S1(Oxygen Sensor Heater Circuit Bank 2 Sensor 1), P0135 -HO2S B1S1 (Oxygen Sensor Heater Circuit Bank 1 Sensor 1), P0161 – HO2S B2S2 (Oxygen Sensor Heater Circuit Bank 2 Sensor 2) P0175 system too rich (bank 2), P0030 HO2S Heater Control Circuit (Bank 1, Sensor 1)

Q: How can I trick my check engine light?

You can trick your check engine light by resetting the engine computer; you need to disconnect the negative terminal battery for about 20min, reconnect the battery, and then the check engine light will turn off but could return if there is still an issue with the vehicle system.

Q: What is the code for the bad engine?

The major code for a bad engine is P0300, and this code could be caused by several things ranging from inadequate combustion in the engine to faulty coil drivers, vacuum leaks e.t.c

Q: What is the most common problem when the check engine light comes on?

The most common problems are:

Those are the common problems that get the check engine light illuminated in most vehicles.

Q: Does disconnecting the battery clear codes?

Yes, disconnecting the battery cables clears codes by resetting the ECU itself, but codes will return after some drive cycles if the issue with the vehicle is not solved before clearing the codes.

Q: Where is the fuse for the check engine light?

The check engine light signal is often sent from the ECM to the instrumental cluster/dashboard through communication data lines. Therefore, it does not have a fuse.

Q: Is the engine code the same as VIN?

No, VIN has 11 digits, while the Engine code does not. But the Engine code is the first 3 digits before the 6 digits Engine number. The VIN only gives information about the Vehicle Trim, year of production, body type specification, etc. 

Reading an Engine Code Without a Reader YouTube 

Final Word

Checking scanned codes without a scanner is economical. Still, sometimes it could be more practical as there are situations where you get a check engine light and some other lights illuminated on the dashboard after the vehicle starts. Still, the result of this procedure will indicate no code stored.

In conclusion, this procedure is best for a quick check of diagnostic codes, mainly when you need access to a scanner/code reader. This is not a professional way of diagnosing the vehicle, but it could save you money if done correctly. Always remember, if no code shows up and the check engine light remains illuminated after following the mentioned steps, you may need to get a qualified mechanic who knows other professional tools.

Engr. Omogbolahan Adeosun

Engr. Omogbolahan Adeosun is an automotive mechanic with over nine years’ experience, He is the C.E.O of Invadars Automobile, and hails from Ado-Ekiti, Nigeria. He obtained his Engr. (Hons) degree in mechanical engineering from Federal university Oye-Ekiti, Nigeria. Engr. Omogbolahan Adeosun writings interest areas are mainly automobile with major focus on four-wheeled vehicles. He has worked as a freelancer for over four companies’ home and abroad. He is a member of a notable professional organization Nigerian society of engineers (NSE). And his professional aspiration is setting a pace and example for the upcoming engineers, to invest their time and knowledge in making his country a proud automobile producers.

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