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Joe, ASE Certified Technician
Category: Toyota
Satisfied Customers: 7251
Experience:  ASE, electronics, Marine inboards and electronics, automotive drivability, all around repair tech,
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Victor. I have a 98 Camry 4 cyl - someone gave it to me and

Customer Question

Hi, Victor. I have a 98 Camry 4 cyl - someone gave it to me and I rebuilt the head 2 years ago at which time I also replaced the fuel pump and catalytic converter and both O2 sensors. Since the rebuild it's always had P0171 and P0141 codes turning on the Check Engine light. Last summer it began very hard starting when hot, and now acceleration is poor even in Neutral. Suggestions?
Submitted: 1 year ago.
Category: Toyota
Expert:  Joe replied 1 year ago.


Thank you for allowing me to assist you, my name is Joe and I will be happy to assist you with your concern today.

The p0171 is usually going to be a bad o2 sensor relating to the heater circuit, however the p0141 is related to system running too lean:

A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor.

I would also check your timing and the valves in the head seeing that the head had work done and could likely be related.

Check fuel pressure as well via a fuel pressure tester and use of professional scan tool will greatly help you with diagnosis as being able to watch systems on the same screen. Checking maf etc.

Thank you!
- Joe

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Customer: replied 1 year ago.
Are the codes possibly switched in your first paragraph? The detailed paragraph for P0171 seems to be dealing with lean mixture. Regarding the O2 sensor heater circuit, since I replaced the sensor, what else would cause the code? Thank you.
Expert:  Joe replied 1 year ago.

Correct, my apologies, p0141 is for the heater circuit and the p0171 is related to the lean condition.

O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)

A code P0141 may mean that one or more of the following has happened: open or short to ground in the wiring harness O2 heater circuit wiring high resistance O2 heater element resistance is high Internal short or open in the heater element.

For p0141 make sure the correct sensor was replaced and that the wiring/harness is not at fault.



Customer: replied 1 year ago.
Thank you for your advice on the codes - I hope to put it to use soon as weather allows. The real reason I came to this forum, though, is what I mentioned in the beginning but perhaps did not make clear. Those codes have been present and recurring ever since I got the car but it ran fine for over a year after the head work. Then, during the summer, it got difficult to start when the engine had been running more than a few minutes. Usually I had to let it cool completely down before it would start again. The engine turns over normally. I determined that the spark was fine so I figure it must be fuel, but the maze of emissions controls made me turn to the experts. After a year of that it suddenly developed a new symptom, very poor acceleration even in neutral. It seems to be a bit better when warm, but still not good enough to risk on the roads. Since the codes were there long before those symptoms started I didn't think they were related, although I've replaced the spark plugs, fuel filter, fuel pump, O2 sensors and catalytic converter trying to cure the codes. So, do you have any experience with the hard starting when warm/hot and poor acceleration? Thank you.
Expert:  Joe replied 1 year ago.

Codes can be present as soon as a problem starts to occur, the problem can worsen over time until it is actually something noticeable where as in some cases at first it is not, This is why it is so important we as mechanics tell customers that any time a check engine light comes on it is important to have checked because it could lead to a potentially serious problem(s).

The problem is running lean not rich meaning less fuel per say. This combined with the code which can cause the symptoms the vehicle is showing result in the need of the above testing that I posted.

Of course just to be sure as I stated you would also want to check timing. If these codes were old it is still a problem that needs fixed as it is at least contributing to the problem. If a problem is fixed then most codes after a correct drive cycle will reset if the problem is no longer present unless they are only history codes. You could in deed check fuel such as pressure and if pressure holds and then preform an injector leak down test, this would cause a rich condition if dumping too much fuel not a lean condition.



Customer: replied 1 year ago.
OK, I'm trying to go through the troubleshooting procedures in the OEM repair manual and they often differ depending on if the car has California emissions or not. The emissions sticker on the hood has CAL at the bottom which I assume means California emissions, but I don't know the history of the car (it has 175,000 mi. on it) and it might just have a non-CAL engine. Can you suggest a way I can confirm what emissions package the engine has? Thanks.