P0171-System too lean. Not enough fuel being burned.
ENGINE CONTROL SYSTEM SELF-DIAGNOSTICS -2001 Toyota Corolla S
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DTC P0171 OR P0172: SYSTEM TOO LEAN/RICH
CAUTION: If ECM replacement is instructed in following testing, always ensure
ECM connectors and ground circuits are okay. If either are suspect,
repair and repeat testing to confirm ECM malfunction.
NOTE:
Heated oxygen sensor No. 1 refers to oxygen sensor closest to engine
block. Heated oxygen sensor No. 2 refers to oxygen sensor farthest from engine block.
NOTE:
For component location, see appropriate illustration in THEORY & OPERATION article.
Circuit Description
Fuel trim refers to feedback compensation value compared against basic injection time. Fuel trim includes short-term and long-term fuel trim.
DTC P0171 is set when fuel trim is driven rich beyond a certain value. Possible causes are:
? Exhaust system leak.
? Improper fuel pressure. ? Fuel injector restricted.
? Defective heated oxygen sensor No. 1. ? Defective Mass Airflow (MAF) meter.
? Defective Engine Coolant Temperature (ECT) sensor. ? Vehicle is ran out of fuel.
DTC P0172 is set when fuel trim is driven lean beyond a certain value. Possible causes are:
? Exhaust system leak.
? Improper fuel pressure.
? Fuel injector blocked or leaking.
? Defective heated oxygen sensor No. 1. ? Defective Mass Airflow (MAF) meter.
? Defective Engine Coolant Temperature (ECT) sensor. ? Vehicle is ran out of fuel.
Diagnostic Aids
Using scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.
Diagnosis & Repair
1/3/2012
ENGINE CONTROL SYSTEM SELF-DIAGNOSTICS -2001 Toyota Corolla S
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Question: P0172 Rich Condition
Tech1
1.
Ask customer if vehicle ran out of fuel. If vehicle ran out of fuel, clear DTCs and retest. If vehicle did not run out of fuel, go to next step.
Ensure oil dipstick, oil filler cap, PCV system and all other air induction system components are intact and operating properly. If problem exists, repair as necessary. If problem does not exist, go
to next step.
Connect scan tool to Data Link Connector (DLC) No. 3. See Fig. 1
normal operating temperature. Monitor oxygen sensor output voltage and short-term fuel trim. If scan tool indicates a lean condition (.55 volt or less, +20 trim) or rich condition (.35 volt or more,
-20 trim), go to next step. If scan tool does not indicate a lean condition (.55 volt or less, +20 trim) or rich condition (.35 volt or more, -20 trim), Check heated oxygen sensor No. 1 circuit. See DTC
P0130: HEATED OXYGEN SENSOR NO. 1 CIRCUIT.
Check fuel pressure. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4- CYLINDER article. Fuel pressure should be 44-50 psi (3.1-3.5 kg/cm ) at idle, and should be 21
psi (1.5 kg/cm ) or more for 5 minutes after engine has stopped. If fuel pressure is not as specified, repair as necessary. If fuel pressure is as specified, go to next step.
Check fuel injectors. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4- CYLINDER article. Fuel injector volume should be 3.7-4.5 cu. In. (60-73 cc) every 15 seconds
and difference in volume between each injector should be less than.8 cu. In. (13 cc). Injectors should not leak more than one drop every 12 minutes. If problem exists, repair as necessary. If
problem does not exist, go to next step.
Check Mass Airflow (MAF) meter and Engine Coolant Temperature (ECT) sensor. See ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If
problem exists, replace appropriate component. If problem does not exist, go to next step. Check spark and ignition system. See IGNITION SYSTEMS in BASIC DIAGNOSTIC
PROCEDURES - 4-CYLINDER article. If problem exists, repair as necessary. If problem does not exist, go to next step.
Check exhaust system for leaks. If problem exists, repair as necessary. If problem does not exist, replace ECM.
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. Start engine and warm to
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Wednesday, January 4th, 2012 AT 5:49 AM
