MAF Sensor - MIL ON/DTC's P0171/P0172 Set

Article No.
98-19-8

09/28/98

^ MALFUNCTION INDICATOR LAMP (MIL) - MIL
ILLUMINATED - DIAGNOSTIC TROUBLE CODES
(DTCS) P0171 AND P0172 STORED IN MEMORY -
VEHICLES WITH 2.0L ENGINE

^ LAMP - MALFUNCTION INDICATOR LAMP (MIL)
ILLUMINATED - DIAGNOSTIC TROUBLE CODES
(DTCS) P0171 AND P0172 STORED IN MEMORY -
VEHICLES WITH 2.0L ENGINE

FORD:
1996-98 CONTOUR

LINCOLN-MERCURY:
1996-98 MYSTIQUE

ISSUE

The Malfunction Indicator Lamp (MIL) may be illuminated with Diagnostic Trouble Codes (DTCs) P0171 and P0172 stored in memory. This may be due to silicon contamination of the Mass Air Flow (MAF) sensor.

ACTION

Replace the MAF sensor with a revised MAF sensor. Refer to the following Service Procedure for details.

SERVICE PROCEDURE

1. Use New Generation Star (NGS) Tester or Service Bay Diagnostic System (SBDS) to determine DTC stored in memory.

2. If you have any of the following Heated Exhaust Gas Oxygen (HEGO) DTCs: P0131, P0132, P0133 and P0135, proceed to Powertrain Control/Emissions Diagnosis (PC/ED) Service Manual Pinpoint Test H to diagnose those codes. If DTCs P0171 and P0172 are present without any HEGO codes, DO NOT CHANGE THE HEGO SENSORS, but proceed as follows:

a. Check the air induction system for air leaks or blockages according to PC/ED Service Manual Pinpoint Test HU.

b. At idle, vehicle in NEUTRAL under normal operating temperature and with all accessories OFF, check the following:

^ 1) Check the barometric reading which should be within +/- 8 Hz of the normal reading for your altitude. Determine the normal barometric reading for your altitude by referring to the SBDS cart or by measuring, with an NGS, several good vehicles from your dealership which have been driven that day.

^ 2) Check the MAF voltage which should be no greater than 0.70 volts.

^ 3) Check the long term fuel trim; the NGS Parameter Identification Display (PID) "LONGTI" should not exceed negative 12% (i.e. -13% is out of limit).

3. If two (2) or more of the above IDLE CHECKS are NOT within range, replace the MAF Sensor (F5RZ-12B579-B). If not, proceed to PC/ED Service Manual Pinpoint Test H for P0171 and P0172 codes.

NOTE
THE BAROMETRIC VALUE DISPLAYED ON NGS/SBDS IS INFERRED BY THE POWERTRAIN CONTROL MODULE (PCM). THE PCM CONSIDERS MANY ELECTRONIC ENGINE CONTROL (EEC) INPUT SIGNALS INCLUDING RPM, MAF AND THROTTLE POSITION TO INFER LOCAL BAROMETRIC PRESSURE. THEREFORE, AFTER A MAF IS REPLACED, THE INFERRED BAROMETRIC READING WILL NOT CHANGE UNTIL THE VEHICLE IS DRIVEN LONG ENOUGH TO ALLOW ADAPTIVE STRATEGY TO RELEARN.

PART NUMBER PART NAME

F5RZ-12B579-B Mass Air Flow (MAF) Sensor

OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage And Emissions Warranty Coverage

OPERATION DESCRIPTION TIME

981908A Diagnose And Replace 0.5 Hr.
Mass Air Flow (MAF)
Sensor

DEALER CODING
CONDITION
BASIC PART NO. CODE
12B579 49

OASIS CODES: 206000, 698298