Corolla 2002 Check Engine Light P0171 and P0300

[Marburg]

I have a Corolla that has since Jan been throwing the same 2 codes P0171 and P0300. I have had the following done:

Throttle Body, butterfly valve and MAF sensor replaced
Both O2 sensors replaced (replaced twice)
Heat sensor replaced
Engine gaskets replaced
PCV checked
Fuel Injection system checked and replaced
Switched to different fuel
Spark plugs and wires replaced
4 coil pack replaced

After each repair the light is off until between 50 and 250 miles. Have not replaced ECM

Any ideas what might be wrong

[Clayton1984]

From the FSM:
P0171 -System too Lean. Trouble area:

• Air induction system
• Injector blockage
• Mass air flow meter
• Engine coolant temp. sensor
• Fuel pressure
• Gas leakage on exhaust system
• Open or short in heated oxygen sensor circuit
• Heated Oxygen sensor
• ECM

P0300 - Random/Multiple Cylinder Misfire detected. Trouble Area:

• Open or short engine wire
• Connector connection (seriously?)
• Vacuum hose connection
• Ignition system
• Injector
• Fuel Pressure
• Engine coolant temp. sensor
• Compression pressure
• Valve clearance
• Valve timing
• ECM

[Marburg]

Thanks. Unfortunately on the P0171: all the items suggested have been checked, cleaned or replaced except the ECM. The ECM has not been replaced.

Same thing for P0300: all items have been checked, tested, cleaned or replaced except ECM.

Now after 3 days of having the light on it has suddenly cleared without having anything further done. Possibly a short or a glitch?

Very confused here. This problem has been going on since Jan.

Thanks for everyones help and all suggested appreciated.

Originally Posted by Clayton1984

From the FSM:
P0171 -System too Lean. Trouble area:

• Air induction system
• Injector blockage
• Mass air flow meter
• Engine coolant temp. sensor
• Fuel pressure
• Gas leakage on exhaust system
• Open or short in heated oxygen sensor circuit
• Heated Oxygen sensor
• ECM

P0300 - Random/Multiple Cylinder Misfire detected. Trouble Area:

• Open or short engine wire
• Connector connection (seriously?)
• Vacuum hose connection
• Ignition system
• Injector
• Fuel Pressure
• Engine coolant temp. sensor
• Compression pressure
• Valve clearance
• Valve timing
• ECM

[Marburg]

Need to find out where to get the computer reprogrammed. Anyone have any ides? Houston Texas

Originally Posted by Marburg

Thanks. Unfortunately on the P0171: all the items suggested have been checked, cleaned or replaced except the ECM. The ECM has not been replaced.

Same thing for P0300: all items have been checked, tested, cleaned or replaced except ECM.

Now after 3 days of having the light on it has suddenly cleared without having anything further done. Possibly a short or a glitch?

Very confused here. This problem has been going on since Jan.

Thanks for everyones help and all suggested appreciated.

[jrsmooth]

Hi, did you have your issues fixed? I have a 2000 Corolla with only 70K miles on it, same issue, the engine light came up, and it failed the State of Virginia's emissions test because P0300 and P0171. Any help would be greatly appreciated. Thanks!

[Marburg]

Got the P0171 cleared after changing trottle body, butterfly valve, MAF sensor, O2 sensors (2), heat sensor (1), cleaned fuel injectors, and replaced relay from fuel pump to ECM.

Still getting P0300 random misfire. Early model 2002 and earlier Corollas can not have ECM reprogrammed can only get them replaced. Cost is way too expensive. However, I was told most common cause of P0300 is malfuntion in fuel injector. 2002 has 4 fuel injectors and would have to replace entire set to fix. If that doesn't do it then it is ECM and I can't afford that quotes are anywhere from $800-$1800 for ECM.

Originally Posted by jrsmooth

Hi, did you have your issues fixed? I have a 2000 Corolla with only 70K miles on it, same issue, the engine light came up, and it failed the State of Virginia's emissions test because P0300 and P0171. Any help would be greatly appreciated. Thanks!

[jrsmooth]

Originally Posted by Marburg

Got the P0171 cleared after changing trottle body, butterfly valve, MAF sensor, O2 sensors (2), heat sensor (1), cleaned fuel injectors, and replaced relay from fuel pump to ECM.

Still getting P0300 random misfire. Early model 2002 and earlier Corollas can not have ECM reprogrammed can only get them replaced. Cost is way too expensive. However, I was told most common cause of P0300 is malfuntion in fuel injector. 2002 has 4 fuel injectors and would have to replace entire set to fix. If that doesn't do it then it is ECM and I can't afford that quotes are anywhere from $800-$1800 for ECM.

Hi,

Thank you very much for the quick responds. Wow, that's a lot of money just to fix this. I mean, $1800? I don't think my car is worth that much. This is bad!

[Marburg]

I know my car isn't worth $1800 and so I'm not going to replace the ECM. I'm going to try cleaning fuel injectors and maybe replacing them - much cheaper

I would start by cleaning the fuel injectors and maybe replacing the O2, MAF, sensors and see if that does it. If not, then I would replace the fuel injectors (those go for about $175 each mine has 4)

Originally Posted by jrsmooth

Hi,

Thank you very much for the quick responds. Wow, that's a lot of money just to fix this. I mean, $1800? I don't think my car is worth that much. This is bad!

[jrsmooth]

Originally Posted by Marburg

I know my car isn't worth $1800 and so I'm not going to replace the ECM. I'm going to try cleaning fuel injectors and maybe replacing them - much cheaper

I would start by cleaning the fuel injectors and maybe replacing the O2, MAF, sensors and see if that does it. If not, then I would replace the fuel injectors (those go for about $175 each mine has 4)

How do you clean the fuel injectors? By just buying the bottle fuel injector liquid and pour it in to the gas tank?

Today, I changed my oil, disconnected the battery, the CEL went off. I drove it for about 5 miles, fill up the gas, drove another 3 miles, the CEL light came back on. I have no clue what to do next. What do you think?

[Marburg]

I took mine to an auto mechanic who has the proper equipment to clean the fuel injectors. He then rescanned and cleared the code. BTW--I found out that diconnecting the battery on a Corolla will only temporarily reset the code - it actually has to be removed using a scanner.

Have you changed O2 sensors and heat sensor and MAF sensor? Those are the other parts that can cause this problem. In my case I had changed all those but have not changed the fuel injectors. My Corolla has 4 injectors which cost $174 each.

Unfortunately, the older model Corollas really aren't worth the money being poured into them to fix the problem. I have elected not to replace the injectors and will be looking at buying a new car.

Originally Posted by jrsmooth

How do you clean the fuel injectors? By just buying the bottle fuel injector liquid and pour it in to the gas tank?

Today, I changed my oil, disconnected the battery, the CEL went off. I drove it for about 5 miles, fill up the gas, drove another 3 miles, the CEL light came back on. I have no clue what to do next. What do you think?