What does this combination of symptoms & error codes mean?

[Fotheringay-Phipps]

I have a 2001 Prizm with a bunch of error codes, and while each code has a multitude of possible causes, I'm wondering if the combination of codes can help narrow it down, along with the symptoms.

There's actually only one symptom: a precipitous drop in gas mileage. Typically over 300 miles before the fuel warning light comes up, but the last couple of tanks this has dropped to about 200. Otherwise the car seems to drive fine.

I hooked up a basic OBD tester I have and came up with the following codes:

P0125
P0171
P1349

And the following "pending codes"

P0130
P0133
P0171

From looking around it seems to me like 0125 relates to a possible thermostat issue, 0130 and 0133 indicate an oxygen sensor or the like, 0171 to a possible MAF sensor or something related, and 1349 indicates a VVT issue. But I'm aware that many of these things are inter-related.

The coolant level is full, the engine oil level is fine, the air filter is OK. I took out the MAF sensor and soaked it in isopropyl alcohol (the local stores are out of MAF cleaner) let it dry and reinstalled it this morning. (My wife drove it since then and said it might be driving a bit smoother but she wasn't sure. It seemed to me like the soaking cleaned it somewhat, but I don't know what a clean MAF sensor is supposed to look like, so not really sure.)

Anyway, my question is: based on the combination of codes and symptoms, can someone make an educated guess as to what is the underlying issue?

Thanks.

[Blue Bowtie]

Can you read live data with your scanner? If so, it would be interesting to see what the PCM is reading as the coolant temperature. That could implicate the CTS and its circuit.

P0125 - Insufficient Coolant Temp For Closed Loop

P0130 - O2 Circuit (Bank 1, Sensor 1) lean

P0133 - O2 Circuit Slow Response

The 130/133 could be the result of the PCM not achieving closed loop mode and trimming fuel appropriately.

[Fotheringay-Phipps]

I have an unsophisticated code-reader. The only thing it really does is read the codes.

From looking around, my guess is that it would be the front (pre-converter) 02 sensor, since that's the only common denominator I see from all the various codes. But that's just a guess.

[I was thinking of replacing it and seeing what happens, but looking at it in the car, it seems very hard to access and the bolts holding it in seem very rusted which would make it even harder, so not going to try it.]

[Blue Bowtie]

Keep in mind that until the PCM achieves closed loop mode, fuel trims are likely going to be based upon a lookup table and not based on O² and other inputs. Without sufficient coolant temperature (or the PCM thinking it's sufficient) it may never be resolved. Since that's probably the easier item to diagnose and repair, and since it will have to be done eventually to clear all the codes anyway, starting there could make sense.

[Stealthee]

A faulty coolant temp sensor will cause a fuel dump. I've seen it so bad that the vehicle wouldn't even run.

[Fotheringay-Phipps]

Brought it into Meineke. They say it's both an O2 sensor and a VVT issue. (~$500)

[Blue Bowtie]

A 2001 Geo has a cam phaser?

[Stealthee]

They were Toyota engines. Apparently yes they had cam phasers too. They can be had for $50 or less. Also the P1349 can be tripped by the phaser simply being dirty.

[Blue Bowtie]

I understand that many cam phasers are sensitive to oil condition. It seemed to be a common malady on some early GM versions. I just didn't know the joint venture engine had them that far back.

[Stealthee]

Originally Posted by Blue Bowtie

I understand that many cam phasers are sensitive to oil condition. It seemed to be a common malady on some early GM versions. I just didn't know the joint venture engine had them that far back.

It kinda shocked me too.

[Fotheringay-Phipps]

I'm a bit unclear about all this. Is the fact that it had a VVT solenoid an indicator that the trouble was with the cam phaser?

The Chevy Prizm from 1998-2002 (& possibly earlier) is a rebadged Toyota Corolla for those years, and all significant parts are therefore identical. (I believe the radio is different, and I know the seatbelts are not compatible, and the like - small trim stuff. But any fundamental component is the same as a Corolla.)

[Stealthee]

No it just odd that there was vvt in an economy car in that era