Trouble shoot low fuel economy

There is NO mileage interval for changing sensors,you would normally get a "check engine" light if a oxygen sensor goes bad.They can get lazy and if your fuel mileage is bad,you would have the vehicle hooked to a scan tool and all systems including oxygen sensors looked at.Many other factors can cause low fuel economy.A full scan would be first on the list.

Considering the age of your car I suggest first having the injectors checked and the fuel pressure regulator.

There might be no trouble there but if they aren't in good order it will be difficult to get a pass and any new parts such as oxygen sensor and/or cat will have a much shortened life and the engine is likely to give low mileage and lower performance.

You should also have the engine thermostat checked and if necessary replaced to ensure a complete warm-up. The temperature sensors and air metering system could also be rather tired and sending misleading information to the engine ECU.

A new cat and an oxygen sensor would probably produce a test pass but would be a false economy without ensuring the basics are ok first.

only the mechanic can answer that, he's the one looking at the car. If he diagnosed a bad valve, get it fixed., then see if it made a difference.

P0135 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

This code refers to the front oxygen sensor on Bank 1. The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The ECM tracks how long it takes for the oxygen sensor to begin switching. It the ECM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135.

Symptoms: You will likely notice poor fuel economy the illumination of the MIL.

Causes: A code P0135 may mean that one or more of the following has happened:
* O2 Heater element resistance is high
* Internal short or open in the heater element
* O2 heater circuit wiring high resistance
* open or short to ground in the wiring harness

Possible Solutions:
* Repair short or open or high resistance in wiring harness or harness connectors
* Replace oxygen sensor (cannot repair open or short that occurs internally to sensor)


I hope this helps, remmeber to rate and comment this.

Sounds like you might have an oxygen sensor problem. Your catalytic converter(s) maybe defective or dirty. That in turn can dirty up the oxygen sensor. A defective oxygen sensor will send faulty info to the computer, interpreting the fumes as cold (even when the engine warms up). That causes the computer to adjust the fuel mixture to very rich, giving you poor gas mileage and the fuel smell. Hope it helps.

Hi Galant5Rov,

Firstly, congratulations to you on identifying the Trouble Code. This code relates to the Heated Oxygen Sensor (H02s)

The oxygen sensors supply the computer with a signal that indicates a rich or lean condition during engine operation (i.e. fuel/air metering).

This input information assists the computer in determining the proper air/fuel ratio. A low voltage signal from one or more sensors indicates too much oxygen in the exhaust (lean condition) and, conversely, a high voltage signal indicates too little oxygen in the exhaust (rich condition).

The oxygen sensors are threaded into the exhaust manifold and/or exhaust pipes on all vehicles.

A faulty oxygen sensor due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit can cause the following symptoms.
Related Symptoms

• Surging at idle
• Unstable idle
• Running rough off idle
• Hesitation
• Stumble
• Chuggle
• Poor fuel economy
• Spark knock
• Stalling on acceleration

You must take EXTREME care when removing these sensors, as they can be difficult to remove (seize up). You may require a special tool to remove these without causing damage to the sensor.

Cheers,


"If this has helped you in any way, please rate this solution" :-)

Usually horrible fuel economy comes from bad oxygen sensors, especially if the engine runs well. Oxygen sensors tell the engine how much fuel to add to the air it's taking in based on how much oxygen is making it out the exhaust. When they go bad, typically the computer's telling the injectors to dump tons of fuel into the engine, because it thinks there's too much oxygen making it through, meaning a lean mixture. They're normally good for about 100,000 miles on modern GM vehicles. and are easy to replace. You have 2 of them that matter for this purpose; one on each y-pipe, between the exhaust manifold and the junction of the "Y" before the catalytic converter. You will need to replace both. They look like a spark plug with a bundle of 4 wires to lead to the engine compartment. If you lay down and slide under the truck right behind the front wheels and look up, you should be staring right at the sensor. The best method of replacing is with a special socket that you can get at any parts store that allows the wires to exit the side of the socket. You do have a total of 4 of these sensors; 2 in front of the catalytic converter in the y-pipes, and 2 after the cat. The two after have no effect on the mixture; they are only for the emissions controls. Finally, 90% of the time, O2 sensors are responsible for poor fuel economy and poor emissions.

DTC - 15 Engine coolant temp sensor error (low temp indicated)
DTC - 22 Throttle position sensor error (signal low)
DTC - 33 MAP sensor circuit error (signal high indicating low vacuum)
DTC - 34 MAP sensor circuit error (signal low indicating high vacuum)
DTC - 44 Oxygen sensor error (lean condition indicated)
DTC - 53 Digital EGR Valve solenoid 1 error

MAP is short for manifold absolute pressure sensor,,it senses the manifold pressure and applies the right amount of gas with the right amount of ignition timing so the car runs and performs well if this does not work properly,it throws off the whole loop cycle for the computer,,which in turn makes it run badly,,and get poor fuel economy,,it causes one to have a lack of power,,combined with a loss of fuel economy,,and also poor take offs,,and sometimes an occasional stalling,,i hope this helps.

EGR system was really developed for was emissions control. the purpose of the EGR valve is to regulate the amount of exhaust gas recirculated back into your combustion chamber to send the gasses through another cycle in order to eliminate any excess pollutants like NOX (nitrogen oxides), N2 (nitrogen), O2 (oxygen), CO2(carbon dioxide) and HC (Hydrocarbons). the EGR was also developed to lower combustion temps that's another reason why the exhaust is recirculated the exhaust gasses will not burn therefor lowering combustion temps, because there is less "usable" air going into the cylinders.

Trouble Code: P0171 (3.8L V6 VIN 1 Auto)
Fuel Trim System Lean (Bank 1) Print this code data Number of Trips to Set Code: 2
OBD II Monitor Type: CCM Details
Indicators: MIL Details

• Fuel Details
• MIL Details

Trouble Code Conditions:
DTC P0101-P0103, P0107, P0108, P0121-P0123, P0130-P0138, P0140, P0141, P0201-P0206, P0300, P0401-P0405, P0410, P0440-P0446, P0506, P0507, P1404 or P1441 not set, engine started, vehicle driven at less than 82 mph at 550-4000 rpm, BARO sensor over 70 kPa (10.1 psi), ECT sensor from 68-230ºF, IAT sensor from 64-158ºF, MAF sensor from 2.8-150 gm/s, MAP sensor from 16-105 kPa (2.6-15.2 psi), fuel level over 10%, and the PCM detected the Long Term fuel trim value was more than +20% for 6 seconds. The PCM controls the air/fuel metering system to good overall fuel economy, driveability, and emission control. During open loop, the PCM determines fuel delivery based on sensor signals, without the oxygen sensor input. During closed loop, the PCM adds oxygen sensor inputs to calculate Short and Long term fuel trim fuel delivery adjustments. Short Term fuel trim values change rapidly in response to changes in the oxygen sensor signals. Long Term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1.

Possible Causes:

• Air leaks in intake manifold, exhaust pipes or exhaust manifold
  
• Fuel control sensor is out of calibration (ECT, IAT or MAF)
  
• Low fuel pressure (fuel filter clogged, pressure regulator failure)
  
• One or more injectors restricted or pressure regulator has failed
  
• HO2S element is contaminated, deteriorated or has failed
  
• Vacuum hose is disconnected, broken, leaking or loose
  

Troubleshooting:2002 Buick Park Avenue, 3.8L, P0171

You will see shorter service life of those O2 sensors with that kind of mileage. I would also suspect that the injectors are seriously worn if original. a few things to also look at that tend to throw 02 codes:

1: MAP OR MAS sensors,
2. worn timing chain
3: Restricted air intake (filter, or leak between MAS sensor and Intake)
4: Engine coolant thermostat (if the engine never warms fully, the mixture will be overly rich)

The O2 sensors tend to get wiped out by too much or too little fuel, too much in your case. you have to find the problem of fuel delivery or it will kill any O2 sensors you replace.

Have you performed a compression check? in some cases the piston, or rings have failed and allowed a large amount of fuel to enter the crankcase oil.