Engine check light: P0171
10-07-2004 | 01:32 PM
#21
Registered User
Joined: Sep 2003
Posts: 380
Likes: 0
From: Albuquerque, NM
The visible bulby thing on the MAF module is NOT the MAF, it is the IAT (intake air temp sensor). The MAF hotwires (there are 2) are located deep inside the MAF tube thingy.
https://www.yotatech.com/attachment....achmentid=1361
https://www.yotatech.com/attachment....achmentid=1362
I've been using Carb cleaner on mine quite successfully.
https://www.yotatech.com/attachment....achmentid=1361
https://www.yotatech.com/attachment....achmentid=1362
I've been using Carb cleaner on mine quite successfully.
Last edited by Unhappy99; 10-07-2004 at 01:43 PM.
10-07-2004 | 01:59 PM
#22
Contributing Member
Joined: Oct 2002
Posts: 5,089
Likes: 0
From: Duvall, WA
Here's what the Factory Service Manual has to say;
P0171
(DI–193)
System too Lean (Fuel Trim)
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leak on exhaust system
Open or short in A/F sensor (Bank 1 sensor 1) circuit
A/F sensor (bank 1 sensor 1)
ECM
CIRCUIT DESCRIPTION
Fuel trim is related to the feedback compensation value, not to the basic injection time. Fuel trim includes short–term fuel trim and long–term fuel trim.
Short–term fuel trim is the short–term fuel compensation used to maintain the air–fuel ratio at its ideal theoretical value. The signal from the A/F sensor is approximately proportional to the existing air–fuel ratio, and ECM compares it with the ideal theoretical value, the ECM reduces fuel volume immediately if the air–fuel ratio is RICH and increases fuel volume if it is LEAN. Long–term fuel trim compensates for the deviation from the central value of the short–term fuel trim stored by each engine tolerance, and the deviation from the central value due to the passage of time and changes of environment.
If both the short–term fuel trim and long–term fuel trim exceed a certain value, it is detected as a malfunction and the MIL lights up.
HINT:
When the DTC P0171 is recorded, the actual air–fuel ratio is on the lean side. When DTC P0172 is recorded, the actual air–fuel ratio is on the rich side.
If the vehicle runs out of fuel, the air–fuel ratio is lean and DTC P0171 is recorded. The MIL then comes on.
If the total of the short–term fuel trim value and long–term fuel trim value is within ± 35 % (80°C (176°F) or more), the system is functioning normally.
The A/F sensor (bank 1 sensor 1) output voltage and the short–term fuel trim value can be read using the OBD II scan tool or TOYOTA hand–held tester.
The ECM controls the voltage of the terminals AF1+ and AF1– of the ECM to the fixed voltage. Therefore it is impossible to confirm the A/F sensor output voltage without OBD II scan tool or TOYOTA hand–held tester.
P0171
(DI–193)
System too Lean (Fuel Trim)
Air induction system
Injector blockage
Mass air flow meter
Engine coolant temp. sensor
Fuel pressure
Gas leak on exhaust system
Open or short in A/F sensor (Bank 1 sensor 1) circuit
A/F sensor (bank 1 sensor 1)
ECM
CIRCUIT DESCRIPTION
Fuel trim is related to the feedback compensation value, not to the basic injection time. Fuel trim includes short–term fuel trim and long–term fuel trim.
Short–term fuel trim is the short–term fuel compensation used to maintain the air–fuel ratio at its ideal theoretical value. The signal from the A/F sensor is approximately proportional to the existing air–fuel ratio, and ECM compares it with the ideal theoretical value, the ECM reduces fuel volume immediately if the air–fuel ratio is RICH and increases fuel volume if it is LEAN. Long–term fuel trim compensates for the deviation from the central value of the short–term fuel trim stored by each engine tolerance, and the deviation from the central value due to the passage of time and changes of environment.
If both the short–term fuel trim and long–term fuel trim exceed a certain value, it is detected as a malfunction and the MIL lights up.
HINT:
When the DTC P0171 is recorded, the actual air–fuel ratio is on the lean side. When DTC P0172 is recorded, the actual air–fuel ratio is on the rich side.
If the vehicle runs out of fuel, the air–fuel ratio is lean and DTC P0171 is recorded. The MIL then comes on.
If the total of the short–term fuel trim value and long–term fuel trim value is within ± 35 % (80°C (176°F) or more), the system is functioning normally.
The A/F sensor (bank 1 sensor 1) output voltage and the short–term fuel trim value can be read using the OBD II scan tool or TOYOTA hand–held tester.
The ECM controls the voltage of the terminals AF1+ and AF1– of the ECM to the fixed voltage. Therefore it is impossible to confirm the A/F sensor output voltage without OBD II scan tool or TOYOTA hand–held tester.
10-07-2004 | 10:02 PM
#23
Thread Starter
Registered User
Joined: Jul 2003
Posts: 142
Likes: 0
From: Sacramento, Calif.
Unhappy99::
Oh no...I did not clean the right thing...so there definitely a hope for this! thanks so much for the pics...they're surely worth 2000 words. I will clean that thing tomorrow afternoon and see how it goes.
WATRD:: thanks for the desc. it's a great way to get started.
Nam
Oh no...I did not clean the right thing...so there definitely a hope for this! thanks so much for the pics...they're surely worth 2000 words. I will clean that thing tomorrow afternoon and see how it goes.
WATRD:: thanks for the desc. it's a great way to get started.
Nam
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