Hi, the problem may be at the TPS or the MAP sensor. First extract the trouble code following instructions below. Then troubleshoot the indicated signals/sensors.
Fig. Fig. 1: ALDL connector-1994 models
Listings of the trouble for the various engine control system
covered in this guide are located in this section. Remember that a code
only points to the faulty circuit NOT necessarily to a faulty component.
Loose, damaged or corroded connections may contribute to a fault code
on a circuit when the sensor or component is operating properly. Be sure
that the components are faulty before replacing them, especially the
expensive ones. The Assembly Line Diagnostic Link (ALDL) connector or
Data Link Connector (DLC) may be located under the dash and sometimes
covered with a plastic cover labeled DIAGNOSTIC CONNECTOR.
-
On all 1994 models the diagnostic trouble codes can be read by grounding test terminal
B
. The terminal is most easily grounded by connecting it to terminal
A
(internal ECM ground). This is the terminal to the right of terminal B on the top row of the ALDL connector.
-
Only 1995 models equipped with a PCM use the OBD I system.
All other 1995 and later models use the OBD II system. The diagnostic
trouble codes on 1995 OBD I systems can be read by grounding test
terminal
6
. The terminal is most easily grounded by connecting it to terminal
5
(internal ECM ground).
-
Once the terminals have been connected, the ignition switch must be moved to the
ON
position with the engine not running.
-
The Service Engine Soon or Check Engine light should be flashing. If it isn't, turn the ignition
OFF
and remove the jumper wire. Turn the ignition
ON
and confirm that light is now on. If it is not, replace the
bulb and try again. If the bulb still will not light, or if it does not
flash with the test terminal grounded, the system should be diagnosed by
an experienced driveability technician. If the light is OK, proceed as
follows.
-
The code(s) stored in memory may be read through counting the
flashes of the dashboard warning lamp. The dash warning lamp should
begin to flash Code 12. The code will display as one flash, a pause and
two flashes. Code 12 is not a fault code. It is used as a system
acknowledgment or handshake code; its presence indicates that the VCM
can communicate as requested. Code 12 is used to begin every diagnostic
sequence. Some vehicles also use Code 12 after all diagnostic codes have
been sent.
-
After Code 12 has been transmitted 3 times, the fault codes, if
any, will each be transmitted 3 times. The codes are stored and
transmitted in numeric order from lowest to highest.
The order of codes in the memory does not indicate the order of occurrence.
-
If there are no codes stored, but a driveability or emissions
problem is evident, the system should be diagnosed by an experienced
driveability technician.
-
If one or more codes are stored, record them. Refer to the applicable Diagnostic Code chart in this section.
-
Switch the ignition
OFF
when finished with code retrieval or scan tool readings.
MAP sensor tests:
TESTINGSee Figures 1, 2 and 3
Fig. Fig. 1: Typical Manifold Absolute Pressure (MAP) sensor
wiring diagram (wire color, terminal identification/location may vary on
certain models)
-
Backprobe with a high impedance voltmeter at MAP sensor terminals
A
and
C
.
-
With the key
ON
and engine off, the voltmeter reading should be approximately 5.0 volts.
-
If the voltage is not as specified, either the wiring to the MAP
sensor or the VCM may be faulty. Correct any wiring or VCM faults before
continuing test.
-
Backprobe with the high impedance voltmeter at MAP sensor terminals
B
and
A
.
-
Verify that the sensor voltage is approximately 0.5 volts with the engine not running (at sea level).
-
Record MAP sensor voltage with the key
ON
and engine off.
-
Start the vehicle.
-
Verify that the sensor voltage is greater than 1.5 volts (above the recorded reading) at idle.
-
Verify that the sensor voltage increases to approximately 4.5. volts (above the recorded reading) at Wide Open Throttle (WOT).
-
If the sensor voltage is as specified, the sensor is functioning properly.
-
If the sensor voltage is not as specified, check the sensor and
the sensor vacuum source for a leak or a restriction. If no leaks or
restrictions are found, the sensor may be defective and should be
replaced.
Fig. Fig. 2: Using jumper wires and a high impedance voltmeter
test between MAP sensor terminals A and C with the key ON and engine
off. The voltage should be approximately 5 volts
Fig. Fig. 3: Next test between MAP sensor terminals A and B with
the key ON and engine off. The voltage should be approximately 0.5 volts
MAP sensor
Throttle position sensor test
TESTINGSee Figures 1, 2 and 3
-
Backprobe with a high impedance voltmeter at TPS ground terminal and 5 volt reference signal terminal.
-
With the key
ON
and engine off, the voltmeter reading should be approximately 5.0 volts.
-
If the voltage is not as specified, either the wiring to the TPS
or the VCM may be faulty. Correct any wiring or VCM faults before
continuing test.
-
Backprobe with a high impedance voltmeter at the TP signal terminal and the sensor ground terminal.
-
With the key
ON
and engine off and the throttle closed, the TPS voltage should be approximately 0.5-1.2 volts.
-
Verify that the TPS voltage increases or decreases smoothly as the
throttle is opened or closed. Make sure to open and close the throttle
very slowly in order to detect any abnormalities in the TPS voltage
reading.
-
If the sensor voltage is not as specified, replace the sensor.
Fig. Fig. 1: Common Throttle Position Sensor (TPS) wiring diagram
(wire color, terminal identification/location may vary on certain
models)
Fig. Fig. 2: Using jumper wires and high impedance voltmeter, test
between the sensor ground and reference terminals, the voltage should
be approximately 5 volts
Fig. Fig. 3: Next test between the sensor signal and ground
terminals, verify that the TPS voltage increases or decreases smoothly
as the throttle is opened or closed
the 3 oem manual are here, real. cut in 1/3rds called FSM 1 to 3
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