check engine light ISUZU TROOPER 1995 Owner's Guide

DRIVEABILITY AND EMISSIONS 6E2-37
ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
(j) • IGNITION "ON" ENGINE "OFF".
• NOTE "CHECK ENGINE" MALFUNCTION INDICATOR LAMP.
STEADY LIGHT
@ • JUMPER DATA LINK CONNECTOR TERM. "1" TO "3".
• DOES MALFUNCTION INDICATOR LAMP FLASH DTC 127
@ DOES "SCAN TOOL" DISPLAY ENGINE CONTROL MODULE DATA?
REFER TO APPLICABLE DTC CHART. START WITH LOWEST DTC.
CHECK FOR GROUNDED DIAGNOSTIC TEST CKT. USE WIRING DIAGRAM ON CHART A-1.
@ COMPARE "SCAN TOOL" DATA WITH TYPICAL VALUES SHOWN ON FACING PAGE. ARE VALUES NORMAL OR WITHIN TYPICAL RANGES?
REFER TO INDICATED "COMPONENT(S) SYSTEM" CHECKS IN~·.

6E2-38 DRIVEABILITV AND EMISSIONS
CHART A-1
WILL NOT FLASH DIAGNOSTIC TROUBLE CODE (DTC) 12
NO "CHECK ENGINE" MALFUNCTION INDICATOR LAMP (MIL)
Circuit Description:
There should always be a steady "Check Engine" Malfunction Indicator Lamp (MIL), when the ignition is "ON" and
engine stopped. Battery positive
voltage is supplied directly to the light bulb. The Engine Control Module (ECM)
will control the light and turn it "ON" by providing a ground path through the VL T wire from the ECM to the bulb.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD The Test Light provides a ground source to the "Check Engine" MIL. If the circuit is okay the "Check Engine"
MIL should
be "ON" when the terminai"A5" is probed.
® Battery feed terminals "C16" and "B1" are protected by a 30 amp ECM fusible link in relay/fuse center under
the hood near the battery.
If terminals "C16" and "B1" have voltage, the ECM grounds or the ECM are faulty.
® Using a test light connected to 12 volts, probe each of the system ground circuits to be sure a good ground is
present. Refer to the
"ECM Terminal End View" in front of this section for ECM pin locations of ground
circuits.
Diagnostic Aids;
Engine runs OK, check;
• Faulty light bulb.
•
VL T wire open.
• Meter fuse blown. This will result in no oil or generator lights, seat belt reminder, etc.
Engine cranks, but
will not run.
• Continuous battery-fuse or fusible link open. • Ignition RED/GRN wire to ECM open.
• ECM ignition fuse open. • Poor connection to ECM.
• Battery RED/WHT wire to ECM open.
TO FUEL .._..,==~ ,__,__-----, PUMP 15A
RELAY .--------~~-RED/WHT Engine
Control
Module(ECM)
BATIERY VOLTAGE
INPUT
ECM FUSIBLE RED/WHT TO LINK 30A '\.. BATIERY ~ VOLTAGE---BLK!RED ~---.-RED/WHT
TO IGNITION - BLK!YEL ~~~-BLK!YEL --'--'~"'---..__
SWITCH TO EGR VALVE VSV
CANISTER PURGE VSV
SECONDARY INTAKE VSV
REED VALVE VSV TO KS MODULE
LOCATED
PASSENGER
SIDE FENDER CHASSIS GROUND
"CHECK ENGINE"
MALFUNCTION
I/P CONNECTOR INDICATOR LAMP
METER (BLUE)
("";:; TO - BLK!YEL ~(---VEL~(;-VLT IGNITION 7.5A SWITCH
BLK ~ GRN MAIN RELAY
SOCKETEND SPLICES
TO ECM TERM. "D1" ECM SYSTEM GROUND
DATA
LINK CONNECTOR(WHITE)
1/P CONNECTOR
(WHITE)
BA TIERY VOLTAGE INPUT
IGNITION
VOLTAGE INPUT
"CHECK ENGINE"
MALFUNCTION
INDICATOR
LAMP DRIVER
~
DIAGNOSTIC REQUEST INPUT
' VIEW Fig. 6E2-24
./ .................................... __________________________ _

DRIVEABILITV AND EMISSIONS 6E2-39
CHART A-1
WILL NOT FLASH DIAGNOSTIC TROUBLE CODE (DTC) 12
NO 11CHECK ENGINE" MALFUNCTION INDICATOR LAMP (MIL)
CD • IGNITION "OFF".
• DISCONNECT ENGINE CONTROL MODULE (ECM) CONNECTORS.
• IGNITION "ON". • PROBE ECM TERMINAL "A5" WITH TEST LIGHT TO GROUND. IS THE "CHECK ENGINE" MALFUNCTION INDICATOR LAMP "ON"?
FAULTY ECM CONNECTION OR ECM. CHECK:
- METER FUSE. FAUL TV BULB. OPEN IN THE VL T
-WIRE. -OPEN IGNITION FEED TO BULB.
@ • IGNITION "OFF".
®
• DISCONNECT ECM CONNECTORS.
• IGNITION "ON".
• PROBE
ECM TERMINAL "C16", "B1" & "A6" WITH TEST LIGHT
TO GROUND. IS THE LIGHT "ON" FOR ALL THREE (3) CIRCUITS?
REPAIR OPEN IN CIRCUIT
THAT DID NOT LIGHT THE TEST LIGHT. IF A FUSIBLE
LINK OR FUSE WAS BLOWN, LOCATE AND CORRECT THE SHORT TO
GROUND ON THAT CIRCUIT.

6E2-40 DRIVEABILITY AND EMISSIONS
CHART A-2
NO DATA LINK CONNECTOR (DLC) DATA OR
WILL NOT FLASH DIAGNOSTIC TROUBLE CODE (DTC) 12
"CHECK ENGINE" MALFUNCTION INDICATOR LAMP (MIL) "ON" STEADY
Circuit Description:
There should always be a steady "Check Engine" malfunction indicator lamp when the ignition is "ON" and engine
stopped. Battery positive
voltage is supplied directly to the light bulb. The Engine Control Module (ECM) will turn
the
light "ON" by grounding VLT wire at the ECM.
With the diagnostic test terminal grounded, the light should flash a diagnostic trouble code (DTC) 12, followed by
any trouble code(s) stored in memory.
A steady
light suggests a short to ground in the light control VLT wire, or an open in diagnostic ORNIYEL wire.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD If there is a problem with the ECM that causes a "Scan tool" to not read Serial data, then the ECM should not
flash a DTC 12.1f DTC 12 does flash, be sure that the "Scan tool" is working properly on anothervehicle.lfthe
"Scan tool" is functioning properly and ORN/BLK wire is OK, the ECM, may be at fault for the NO data link
connector symptom.
@ If the light goes "OFF" when the ECM connector is disconnected, then, the VLTwire is not shorted to ground.
® This step will check for an open diagnostic request ORN/YEL wire.
® At this point, the "Check Engine" malfunction indicator lamp wiring is OK. The problem is a faulty ECM.IfDTC
12 does not flash, the ECM should be replaced.
TO FUEL PUMP
FUEL RED/BLK ENGINE CONTROL MODULE(ECM)
PUMP 15A
RELAY
,.-------------.--RED/WHT
TO BATTERY
ECM FUSIBLE
LINK 30A
VOLTAGE
...,. .. 1---BLK!RED
TO IGNITION
SWITCH ENGINE
15A
'------RED/WHT
BLK
BLK!YEL
~ BLK!YEL
TO EGA VALVE VSV TO FUEL CANISTER PURGE VSV INJECTORS ..._ ___ RED/GRN
LOCATED
PASSENGER
SIDE
FENDER CHASSIS
GROUND
SECONDARY
INTAKE VSV TO KS ..._ ___ RED/GRN REED VALVE VSV MODULE
"CHECK ENGINE"
MALFUNCTION
liP CONNECTOR INDICATOR
LAMP
METER (BLUE)
f'7:'
TO -----BLK!YEL ~~ YEL ---\C:;J- SWITCH
BLK
GRN
MAIN RELAY SOCKET END VIEW
7.5A
SPLICES TO ECM TERM. "D1" ECM SYSTEM
GROUND
DATA LINK CONNECTOR
(WHITE)
Fig. 6E2-25
I/P CONNECTOR
(WHITE)
BATTERY VOLTAGE
INPUT
BATTERY VOLTAGE
INPUT
IGNITION
VOLTAGE INPUT
"CHECK ENGINE"
MALFUNCTION
INDICATOR
LAMP DRIVER
~
DIAGNOSTIC
REQUEST INPUT

®
.... /"{ rtS (ill .. , (. --f (.'' \J DRIVEABILITV AND EMISSIONS 6E2-41
CHART A-2
NO DATA LINK CONNECTOR (DLC) DATA OR
WILL NOT FLASH DIAGNOSTIC TROUBLE CODE (DTC) 12
"CHECK ENGINE" MALFUNCTION INDICATOR LAMP (MIL) "ON" STEADY
• IGNITION "ON", ENGINE "OFF". IS THE "CHECK ENGINE" MALFUNCTION INDICATOR LAMP (MIL) "ON"?
~ $
• GROUND DATA LINK CONNECTOR, DIAGNOSTIC USE CHART A-1 I TERMINAL "1" AND "3". DOES LIGHT FLASH DIAGNOSTIC TROUBLE CODE (DTC) 12?
$ $
• IGNITION "OFF". G) IF PROBLEM WAS NO DATA LINK CONNECTOR
• DISCONNECT ENGINE CONTROL MODULE (ECM) DATA: CHECK SERIAL DATA CIRCUIT FOR OPEN OR CONNECTORS.
SHORT TO GROUND BETWEEN ECM AND DATA • IGNITION "ON" AND NOTE MIL LINK CONNECTOR. IF OK, IT IS A FAULTY ECM.
I LIGHT "OFF" I LIGHT "ON" j
I • IGNITION "OFF". REPAIR SHORT TO GROUND IN MIL CIRCUIT.
• RECONNECT ECM.
• IGNITION "ON", ENGINE "OFF",
DIAGNOSTIC TEST TERMINAL NOT GROUNDED.
• BACK
PROBE ECM TERMINAL "C4" WITH TEST
LIGHT TO GROUND.
LEAVE CONNECTED AND WATCH MIL.
I NO DTC 12 I DTC 12 I
I REPLACE ECM I CHECK FOR OPEN IN ORNIYEL WIRE. IF OK, CHECK FOR OPEN CIRCUIT BETWEEN DATA LINK CONNECTOR TERMINAL "3" AND GROUND.
CLEAR DTC(S) AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL"CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.

6E2-42 DRIVEABILITV AND EMISSIONS
CHART A-3
(Page 1 of 3)
ENGINE CRANKS BUT WILL NOT RUN
Circuit Description:
Before using this chart, battery condition, engine cranking speed, and fuel quantity should be checked and verified
as being OK.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD A malfunction indicator lamp "ON" is basic test to determine if there is battery positive voltage and ignition
voltage supplied to the Engine Control Module (ECM). No data link connector data may be due to an ECM
problem. CHART A-2 will diagnose the ECM. If throttle position sensor voltage is over 2.5 volts, the engine
may be in the
"clear flood" mode, which will cause starting problems. The engine will not start without
reference pulses and, therefore, the "Scan tool" should indicate engine speed during cranking.
@ Because the electronic ignition system uses two plugs and wires to complete the circuit of each coil, the
opposite spark
should be left connected. If revolution per minute was indicated during crank, the ignition
control module is receiving a crank signal, but no spark at this test indicates the Ignition Control Module (ICM)
is not triggering the coils.
® The test light should blink, indicating the ECM is in control of the injectors. How bright the light blinks is not
important. However, the test light should be a J-34730-3 or equivalent.
@ This test will determine if the ignition control module is not generating the reference pules or if the wiring or
ECM are at fault. By touching and removing a test light to 12 volts on VEL/RED wire, a reference pulse should
be generated. If revolution per minute is indicated, the ECM and wiring are OK.
® High resistance in the spark plug wire could cause a "no start" condition. If a spark plug wire is found to be
faulty, replace it and retest system.
(SOHC)
I"M"
TOECM RED/GRN #1 BLU/YEL MAIN RED/GRN #2 BLU/YEL
RELAY
tRED/GRN
RED/GRN #3 BLU/YEL
RED/GRN #4 BLU/YEL
RED/GRN
#5 BLU/YEL
RED/GRN
#6 BLU/YEL
FUEL
INJECTORS ENGINE
CONTROL MODULE(ECM)
INJECTOR
RED/GRN
RED/GRN
RED/GRN
RED/GRN
RED/GRN
RED/GRN
IDOHCI BLU/YEL
BLU/YEL
l 1.3!l INJECTOR RESISTOR 1_
ORG/BLU
--+----
E~INE YEL/GRN D11 BLK/ORN -4>-BLK/YEL ----41sv---TO IGN BLK/RED -TOTACHOMETER SWITCH
BLK --:::L =
AND TCM (C91-D12)
CRANKSHAFT
POSITION
1 SENSOR
-........:::SHIELD
Fig. 6E2-26
•

DRIVEABILITY AND EMISSIONS 6E2-43
CHART A-3
-JJ!atfe 1 of 3)
ENGINE CRANKS BUT WILL NOT RUN
Q) • IGNITION "ON", IF "CHECK ENGINE" MALFUNCTION INDICATOR LAMP IS "OFF", SEE CHART A-1. • INSTALL TECH 1 "SCAN TOOL". IF "NO DATA LINK CONNECTOR", SEE CHART A-2. • CHECK THE FOLLOWING: THROTTLE POSITION SENSOR-IF OVER 2.5V AT CLOSED THROTTLE, SEE DIAGNOSTIC
TROUBLE CODE 21. IS REVOLUTION PER MINUTE INDICATED DURING CRANKING?
® • USING AN ST-125 (SPARK CHECKER) CHECK FOR SPARK ON TWO WIRES (2-4 OR 4-6).
® • USING AN ST-125 (SPARK CHECKER) J-26792 OR EQUIVALENT, CHECK FOR SPARK ON TWO WIRES (2-4 OR 4-6).
• CHECK ONE WIRE AT A TIME. LEAVE THE OTHER WIRES CONNECTED TO SPARK PLUG
WHILE CRANKING.
IS THERE SPARK ON BOTH
WIRES?
@ • DISCONNECT THE ENGINE HARNESS BLACK CONNECTOR
(DOHC) OR BLUE CONNECTOR (SOHC).
• USING A TEST LIGHT CONNECTED TO BATTERY POSITIVE VOLTAGE. • PROBE THE BLUIYEL
WIRE AT THE BLACK CONNECTION AND THE
BLU/GRN WIRE AT THE BLUE CONNECTOR
WHILE CRANKING THE ENGINE.
TEST LIGHT SHOULD
BLINK ON BOTH, DID
IT?
FAULTY IGNITION
MODULE
REFER TO L-----------1 CHART A-3
~20F3)
• CHECK ONE WIRE AT A TIME. LEAVE THE OTHER WIRES CONNECTED TO SPARK PLUG WHILE CRANKING. IS THERE SPARK ON BOTH WIRES?
NO SPARK
@ • IGNITION "OFF". SEE CHART A-3 (eA8£3 OF 3)
SPARK ON ONE
@ CHECK PAIR OR WIRES THAT DID
NOT SPARK.
EACH WIRE SHOULD MEASURE
LESS THAN 30,000 OHMS. IF OK, SWITCH COIL
ASSEMBLIES. DOES PROBLEM MOVE? •
DISCONNECT IGNITION
6-WAY CONNECTOR.
• IGNITION "ON". • MOMENTARILY TOUCH VEL/RED WIRE WITH A TEST
LIGHT TO 12 VOLTS WHILE
OBSERVING ENGINE SPEED.
IS REVOLUTION PER MINUTE
INDICATED?
VEL/RED WIRE OPEN OR SHORTED TO
GROUND
OR FAULTY ENGINE
CONTROL MODULE
CLEAR DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION
INDICATOR LAMP OPERATION.

DRIVEABILITV AND EMISSIONS 6E2-45
CHART A-3
.(hfi 2 of 3)
ENGINE CRANKS BUT WILL NOT RUN
FROM CHART A-3 (1 OF 3) I l j_ I
BLINKING LIGHT I STEADY LIGHT I NO LIGHT j
I
I @ • RECONNECT THE BLUE AND @ • IGNITION "OFF". •
BACK PROBE ECM AT TERMINAL BLACK ENGINE HARNESS • DISCONNECT ENGINE CONTROL C11,
C14, D15 AND D16 WITH
CONNECTORS. MODULE (ECM) CONNECTORS. TEST LIGHT TO BATTERY • REFER TO $E.CR01111:2 FOR • PROBE ECM TERMINALS C11, POSITIVE
VOLTAGE.
INTAKE PLENUM REMOVAL. C14, D15 AND D16 WITH TEST •
NOTE LIGHT WHILE CRANKING,
• WITH INTAKE PLENUM REMOVE LIGHT TO BATTERY POSITIVE SHOULD
BLINK.
DISCONNECT AND CHECK AT VOLTAGE. DOES IT? LEAST TWO INJECTORS
WITH LIGHT
SHOULD BE "OFF" ON ALL
THE INJECTOR TEST LIGHT TERMINALS. J34730-B. IS IT? TESTER SHOULD BLINK WHILE I CRANKING ENGINE.
~ ~ ~ $
DOES IT?
SHORT TO GROUND IN I FAULTY I
OPEN IN INJECTOR II FAUL TV
J CIRCUIT THAT LIGHT ECM DRIVER CIRCUIT(S). ECM WAS "ON".
~ $
• CHECK RESISTANCE OF @ • IGNITION "ON". INJECTORS, SHOULD BE 1.2 -3.0 • TEST LIGHT CONNECTED TO GROUND.
OHMS. • PROBE RED/GRN WIRE AT ANY INJECTOR.
• REPLACE ANY INJECTOR THAT LIGHT SHOULD BE "ON". WAS NOT CORRECT. IS IT? IF ALL WERE OK, REFER TO I CHART A-7 TO TEST FUEL
$ ~
PRESSURE.
• TEST LIGHT CONNECTED TO OPEN IN CIRCUIT BATTERY POSITIVE VOLTAGE BETWEEN INJECTORS PROBE BLUIYEL (DOHC} WIRE OR AND ECM MAIN BLU/YEL, ORG/BLU AND BLU/GRN RELAY. (SOHC) OF ANY INJECTOR.
NOTE LIGHT WHILE CRANKING
THE ENGINE.
LIGHT SHOULD "BLINK".
DOES
IT?
I
$
I
I NO (SOHCll NO (DOHC)j
®
I REFER TO CHART A-7 TO
I
• IGNITION "OFF". TEST FUEL PRESSURE. • DISCONNECT INJECTOR
RESISTOR MODULE.
• USING
DVOM MEASURE RESISTANCE OF THE MODULE BETWEEN THE BLU/YEL WIRE AND THE BLU/GRN WIRE.
SHOULD HAVE 2.7 OHMS ±10%. DOES IT?
$ $
REPAIR OPEN REPLACE INJEC-IN THE INJEC- TOR
RESISTOR
TOR DRIVER MODULE
CIRCUIT(S).

DRIVEABILITV AND EMISSIONS 6E2-51
CHART A-7
(PJtge 1 of 3}
FUEL SYSTEM PRESSURE TEST
NOTE: FUEL SYSTEM IS UNDER PRESSURE. TO AVOID FUEL SPILLAGE, REFER TO FIELD SERVICE PROCEDURES FOR TESTING OR REPAIRS
REQUIRING DISASSEMBLY OF FUEL LINES OR FITTINGS. REFER TO~ 3 OF 3 OF THIS CHART.
CD • INSTALL FUEL PRESSURE GAUGE, J34730-1 OR EQUIVALENT, SEE CHART A-7 ~3 OF 3) FOR INSTALLATION PROCEDURE.
• DISCONNECT VACUUM HOSE FROM FUEL PRESSURE CONTROL VALVE.
• IGNITION MUST BE "OFF" FOR 10 SECONDS.
• TURN IGNITION "ON". FUEL PUMP SHOULD RUN FOR ABOUT 2 SECONDS.
• NOTE FUEL PRESSURE AFTER PUMP STOPS.
• FUEL PRESSURE SHOULD BE 280-320 kPa (41-46 PSI) AND HOLDING STEADY. IS IT?
I
• START AND IDLE ENGINE AT NORMAL OPERATING TEMPERATURE. • RECONNECT VACUUM LINE.
• FUEL PRESSURE SHOULD HAVE
DROPPED SLIGHTLY.
DID IT?
I
@ FUEL PRESSURE
WITHIN SPECIFICATION,
BUT NOT HOLDING.
• IGNITION "OFF".
.---'---$YES
-$r---'--NO -
@ • DISCONNECT VACUUM NO TROUBLE •
CONNECT FUSED
JUMPER FROM BATTERY POSITIVE
VOLTAGE TO FUEL PUMP
RELAY CONNECTOR BETWEEN THE BLK/RED WIRE AND RED/WHT WIRE IN ENGINE
COMPARTMENT.
HOSE FROM
FUEL FOUND. REFER PRESSURE CONTROL TO "DIAGNOSTIC
VALVE. AIDS" ON
• WITH ENGINE IDLING. FACING P.A@f. APPLY 12-14"
HYDRAGYRUM OF VACUUM TO FUEL PRESSURE CONTROL
VALVE
•
FUEL PRESSURE SHOULD DROP SLIGHTLY.
DID IT?
I
• GRADUALLY BLOCK FUEL PRESSURE LINE BY PINCHING FLEX HOSE.
• REMOVE JUMPER FROM
TEST CONNECTOR WHILE
CONTINUING TO BLOCK
PRESSURE LINE.
• PRESSURE SHOULD HOLD.
DID
IT?
I PRESSURE
OUT OF SPECIFICATION.
I USE,.eAef 2 OF THIS CHART.
I
INO I PRESSURE
I
I USE CHART I A-5
~~NLO------------------~ $~YELS---------------------, LOCATE AND CORRECT
CAUSE OF INTERRUPTED
MANIFOLD ABSOLUTE
PRESSURE SUPPLY TO
REGULATOR. FUEL PRESSURE
CONTROL VALVE ASSEMBLY
IS FAULTY.
• REPEAT ABOVE PROCEDURE CHECK FOR WHILE BLOCKING FUEL -LEAKING PUMP COUPLING HOSE. RETURN LINE INSTEAD OF -FAUL TV IN-TANK PUMP PRESSURE LINE BY PINCHING FLEX HOSE.
• PRESSURE SHOULD HOLD.
DID
IT?
LOCATE AND REPLACE LEAKING INJECTOR AND DRY SPARK PLUGS
FROM FLOODED
CYLINDERS.
FUEL PRESSURE
CONTROL VALVE
ASSEMBLY
IS FAULTY.

®
DRIVEABILITY AND EMISSIONS 6E2-65
DIAGNOSTIC TROUBLE CODE (DTC) 21A
THROTILE POSITION (TP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE HIGH)
• KEY "ON" ENGINE "OFF". • THROTTLE CLOSED.
DOES "SCAN TOOL" DISPLAY THROTTLE POSITION
(TP) SENSOR OVER 2.5 VOLTS?
$ $
• DISCONNECT SENSOR, "SCAN TOOL" SHOULD • THROTTLE AT WIDE OPEN POSITION. DOES SCAN
DISPLAY TP SENSOR BELOW .2 VOLT (200mV}. TOOL DISPLAY TP SENSOR AT 4.0 VOLTS OR
DOES IT? MORE?
I
$ cvr
REFER TO DIAGNOSTIC DTC 21 IS
INTERMITTENT.
TROUBLE CODE (DTC} IF NO ADDITIONAL DTC(S} 21 B WERE STORED, REFER TO
"DIAGNOSTIC AIDS" ON FACING~.
~ $
• PROBE SENSOR GROUND CIRCUIT TP SENSOR SIGNAL CKT SHORTED TO VOLTAGE
WITH A TEST LIGHT CONNECTED TO OR BATTERY POSITIVE VOLTAGE. FAULTY ENGINE CONTROL MODULE.
I LIGHT "ON" I LIGHT "OFF" I
I FAULTY CONNECTION
OPEN SENSOR GROUND CIRCUIT OR
OR SENSOR. FAULTY ENGINE CONTROL MODULE.
CLEAR DTC(S}
AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.