1988 PONTIAC FIERO Service Repair Manual

CODE 43
ELECTRONIC SPARK CONTROL (ESC) CIRCUIT
5.0L (VIN E) "F" SERIES (TBI)
Circuit Description:
Electronic spark control is accomplished with a module that sends a voltage signal to the ECM. As the
knock sensor detects engine knock, the voltage from the ESC module to the ECM drops, and this signals the
ECM to retard timing. The ECM will retard the timing when knock is detected and rpm is above about 900
rpm. Code 43 means the ECM has been low voltage at CKT 485 terminal
"B7" for longer than 5 seconds with the
engine running or the system has failed the functional check.
This system performs a functional check once per start up to check the ESC system. To perform this test the
ECM will advance the spark when coolant is above 95°C and at
a high load condition (near W.O.T.). The ECM
then checks the signal at
"B7" to see if a knock is detected. The functional check is performed once per start up
and if knock is detected when coolant is below 95°C (194°F) the test has passed and the functional check will not
be run. If the functional check fails, the "Service Engine Soon" light will
remain "ON" until ignition is turned
"OFF" or until a knock signal is detected.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. If the conditions for a Code 43 are present the
"Scan" will always display "yes". There should
not be a knock at idle unless an internal engine
problem, or a system problem exists.
2. This test will determine if the system is
functioning at this time. Usually a
knock signal
can be generated by tapping on the block close to
the area of the sensor.
3. Because Code 43 sets when the signal voltage on
CKT 485 remains low this test should cause the
signal on CKT 485 to go high. The
12 volts signal
should be seen by the ECM as "no knock"
it' the
ECM and wiring are OK.
4.
This test will determine if the knock signal is
being detected on CKT 496 or if the ESC module is
at fault. 5.
If
CKT 496 is routed to close to secondary ignition
wires the ESC
module may see the interference as
a knock signal.
6. This checks the ground circuit to the module. An
open ground will cause the voltage on CKT 485 to
be about
12 volts which would cause the Code 43
functional test to fail.
7. Contacting
CKT 496 with a test light to
12 volts
should generate a knock signal.
This will
determine if the ESC nodule is operating
correctly.
Diagnostic Aids:
Code 43 can be caused by a faulty connection at
the knock sensor at the ESC
lnodule or at the ECM.
Also check CKT 485 for possible open or short to
ground.
Iiefer to "Intcrmittents" in Section "B".

DRIVEABILITY AND EMISSIONS 5.OL (VIN E) 6E2-A-47
IN AREA OF KNOCK SENSOR. 5 TERMINAL "C" (CKT
INDICATED WHILE TAPPING
ST LIGHT CONNECTED
AFTER
5 SECONDS, DOES "SCAN"
@ DISCONNECT KNOCK SENSOR.
ENGINE IDLING.
@ MOMENTARILY TOUCH KNOCK
SENSOR HARNESS (CKT496) WITH
A TEST LIGHTTO 12V. @ EACH TIME THE TEST LIGHT
CONTACTS CKT 496, A KNOCK

6E2-A-48 5.OL, (VIN E) DRIVEABILITY AND f MISSIONS
CODE 44
OXYGEN SENSOR CIRCUIT
(LEAN EXHAUST INDICATED)
5.OL (VIN E) "F" SERIES (TBI)
Circuit Description:
The ECM supplies a voltage of about .45 'volt between terminals "D6" and "117". (If measured with a 10
megohmdigital voltmeter, this may readas low as .32 volts.) The 02 sensor varies the voltage within a range of
about
1 volt if the exhaust is rich, down through about .I0 volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below about
360°C (600°F). An open
sensor circuit or cold sensor causes "Open Loop" operation.
Test Description: Numbers below refer to circled @
numbers on the diagnostic chart.
1. Code 44 is set when the 02 sensor signal voltage
on
CK'l' 412.
@ Remains below .2 volt for 50 seconds,
@ And the system is operating in 'qClosk?d Loop". @
@
Diagnostic Aids:
Using the "Scan", observe the block learn values
at different rpm and air flow conditions to determine
@
when the Code 44 may have been set. If the
conditions for Code
44 exists the block learn values
will be around 150.
@ Q2 Sensor Wire Sensor pigtail may be
m?spositioned and contacting the exhaust @
manifold.
@ Check for intermittent ground in wire between
connector and sensor.
@
MAP Sensor A (MAP) sensor output that causes
the ECM to sense a higher than normal vacuum
will cause the
system to go lean. Disconnect the
MAP sensor and
if the lean condition is gone,
replace the sensor.
Lean
Iniectorts)
Fuel Contamination Water, even in small
amounts, near the in-tank fuel pump inlet can be
delivered to the injectors. The water causes
n lean
exhaust and can set a Code
44.
Fuel Pressure System will be lean if pressure is
too low.
It
may be necessary to monitor fuel
pressure while driving the car at various road
speeds
ancUor loads to confirm. See "Fuel System
Diagnosis",
CHART A-7.
Exhaust
Leaks If there is an exhaust leak, the
cngine can cause outside air to be pulled into the
eshaust
and past the sensor. Vacuum or
crankcase leaks can cause a lean condition.
If the above are OK, it is a faulty oxygen sensor.

@ WITH ENGINE IDLING "SCAN" SHOULD DISPLAY O2
SENSOR BETWEEN .35 VOLTS AND .55 VOLTS (350

6EZ-A-50 5.0b (VIN E) DRIVEABILITY AND EMISSIONS
- GROUND -
CODE 45
OXYGEN SENSOR CIRCUIT
(RICH EXHAUST INDICAnEB)
5.OL (VlN E) ""FYESEBIES (TBI)
Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10
megohm digital voltmeter, this may read as low as .32 volts.) The
O2 sensor varies the voltage within a range
of about
1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F). An open
sensor circuit or cold sensor causes "Open Loop" operation.
Test Description: Numbers below refer to circled
numbers on the diagnostic chart.
1. Code 45 is set when the O2 sensor signal voltage or
CKT
422.
@ Remains above .7 volts for 50 seconds; and in
"Closed Loop".
@ Engine time after start is 1 minute or more.
@ Throttle angle greater than 2% (about .2 volts
above idle voltage) but less than 25%.
Diagnostic Aids:
Using the "Scan", observe the block learn values at
different rpm conditions to determine when the
Code
45 may have been set. If the conditions for Code 45
exists, The block learn values will be around 115.
@ Fuel Pressure System will go rich if pressure is too
high. The ECM can compensate for some increase.
However, if it gets too high, a Code 45
may be set.
See "Fuel System Diagnosis", CHART
A-7.
Q See CHART A-7.
@ Check for fuel contaminated oil.
@ HE1 Shielding An open ground CKT 453 (ignition
system ref. low) may result in EMI, or induced
electrical "noise". The ECM looks
at this "noise" as
reference pulses. The additional pulses result in a
higher than actual engine speed signal. The ECM
then delivers too much fuel, causing system to go
rich. Engine tachometer will also show higher than
actual engine speed, which can help in diagnosing
this problem.
@ Canister Purge Check for fuel saturation. If full of
fuel, check canister control and hoses. See
"Canister Purge", Section
"(23".
@ MAP Sensor An output that causes the ECM to
sense a lower than normal
vacuum can cause the
system to go rich. Disconnecting the MAP sensor
will allow the ECM to set
a fixed value for the
sensor. Substitute a different MAP sensor if the the
rich condition is gone while the sensor is
disconnected.
r TPS An intermittent TPS output will cause the
system to go rich, due to
a false indication of the
engine accelerating.

PNWBLK 439
CODE 53
VEHICLE ANTI-THEFT SYSTEM (VATS) CIRCUIT
5.OL (VIM E) "F" SERIES (TBI)
Circuit Description:
The VATS system is designed to disable vehicle operation if the incorrect key or starting procedure is used.
The VATS decoder module sends a signal to the ECM if the correct key is being
:sed. If the proper signal does
not reach the ECM on CKT 963, the ECM will not pulse the injectors
"ON" and thus not allow the vehicle to be
started. Code
53 will set, if the proper signal is not being received at ECM terminal "B6" when the ignition is turned
"ON". Code 53 does not store in the ECM memory but is only present when the conditions stated above are met.
Test Description: Numbers below refer to circled If the decoder module is found to be OK, as
numbers on the diagnostic chart. determined
from Section
"SA", the ECM may be at
1. If the engine cranks, and a Code 53 is stored, it Fault,
but this is not a likely condition.
indicates that the portion of the module which
2. If Code 53 is stored, and the engine will not crank,
generates the signal to the ECM is not operating it indicates
that there is a VATS problem or an
or CKT 963 is open or shorted to ground. incorrect
key or starting procedure is being used.