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ignition on. If scan tool does not display BUS SHORT TO 5 VOLTS,
replace CTM. If scan tool displays BUS SHORT TO 5 VOLTS, go to next
step.
8) Disconnect scan tool from DLC. Using external voltmeter,
measure voltage between ground and DLC connector terminal No. 3
(Violet/Brown wire). If voltage is more than 4 volts, repair
Violet/Brown wire for short to voltage. If voltage is 4 volts or less,
go to next step.
9) Measure voltage between ground and DLC connector terminal
No. 11 (White/Black wire). If voltage is more than 4 volts, repair
White/Black wire for short to voltage. If voltage is less than 4
volts, replace scan tool cable or scan tool as necessary.
10) Turn ignition off. Using external ohmmeter, measure
resistance between Powertrain Control Module (PCM) connector C3
terminal No. 30 (Violet/Brown wire) and connector C1 terminal No. 17
(Violet/Black wire). PCM is located at right inner fender. If
resistance is less than 800 ohms, repair short between Violet/Brown
wire and Violet/Black wire. If resistance is 800 ohms or more, go to
next step.
11) Measure resistance between PCM connector C3 terminal No.
28 (White/Black wire) and PCM connector C1 terminal No. 17
(Violet/Black wire). If resistance is less than 800 ohms, repair short\
between Violet/Black and White/Black wires of both connectors. See
wiring diagram for clarification. If resistance is 800 ohms or more,
replace PCM.
BUS SHORT TO BATTERY
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1 after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) Turn ignition off. Disconnect Powertrain Control Module
(PCM). PCM is mounted in right side of firewall. Turn ignition on. If
scan tool does not display BUS SHORT TO BATTERY, go to step 10). If
scan tool displays BUS SHORT TO BATTERY, go to next step.
2) Turn ignition off. Disconnect instrument cluster. Turn
ignition on. If scan tool does not display BUS SHORT TO BATTERY,
replace instrument cluster. If scan tool displays BUS SHORT TO
BATTERY, go to next step.
3) Turn ignition off. Disconnect compass mini-trip computer.
Turn ignition on. If scan tool does not display BUS SHORT TO BATTERY,
replace compass mini-trip computer. If scan tool displays BUS SHORT TO
BATTERY, go to next step.
4) Turn ignition off. Disconnect CCD radio. Turn ignition on.
If scan tool does not display BUS SHORT TO BATTERY, replace radio. If
scan tool displays BUS SHORT TO BATTERY, go to next step.
5) Turn ignition off and wait 2 minutes. Disconnect Air Bag
Control Module (ACM). ACM is located under center of instrument panel.\
Turn ignition on. If scan tool does not display BUS SHORT TO BATTERY,
replace ACM. If scan tool displays BUS SHORT TO BATTERY, go to next
step.
6) Turn ignition off. Disconnect Central Timer Module (CTM).\
CTM is located under left side of instrument panel. Turn ignition on.
If scan tool does not display BUS SHORT TO BATTERY, replace CTM. If
scan tool displays BUS SHORT TO BATTERY, go to next step.
7) Turn ignition off. Disconnect anti-lock brake controller
module. Controller module is mounted to top of ABS hydraulic unit.
Turn ignition on. If scan tool does not display BUS SHORT TO BATTERY,
replace anti-lock brake controller module. If scan tool displays BUS

SHORT TO BATTERY, go to next step.
8) Disconnect scan tool from DLC. Using external voltmeter,
measure voltage between ground and DLC connector terminal No. 3
(Violet/Brown wire). If voltage is more than .2 volt, repair
Violet/Brown wire for short to voltage. If voltage is .2 volt or less,
go to next step.
9) Measure voltage between ground and DLC connector terminal
No. 11 (White/Black wire). If voltage is more than .2 volt, repair
White/Black wire for short to voltage. If voltage is less than .2
volt, replace scan tool cable or scan tool as necessary.
10) Turn ignition off. Using external ohmmeter, measure
resistance between ground and Powertrain Control Module (PCM)
connector C1 terminal No. 31 (Black/Tan wire). PCM is located at right\
inner fender, at corner of firewall. If resistance is less than 10
ohms, go to next step. If resistance is 10 ohms or more, repair open
Black/Tan wire.
11) Measure resistance between ground and PCM connector C1
terminal No. 32 (Black/Tan wire). If resistance is less than 10 ohms,
replace PCM. If resistance is 5 ohms or more, repair open Black/Tan
wire.
BUS SHORT TO GROUND
NOTE: For connector terminal identification and wiring diagrams,
see BODY CONTROL COMPUTER - INTRODUCTION article. Perform
VERIFICATION TEST VER-1 after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module
connector.
1) Turn ignition off. Disconnect Powertrain Control Module
(PCM). PCM is mounted in right side of firewall. Turn ignition on. If
scan tool does not display BUS SHORT TO GROUND, replace PCM. If scan
tool displays BUS SHORT TO GROUND, go to next step.
2) Turn ignition off. Disconnect anti-lock brake controller
module. Controller module is mounted to top of ABS hydraulic unit.
Turn ignition on. If scan tool does not display BUS SHORT TO GROUND,
replace anti-lock brake controller module. If scan tool displays BUS
SHORT TO GROUND, go to next step.
3) Turn ignition off. Disconnect instrument cluster. Turn
ignition on. If scan tool does not display BUS SHORT TO GROUND,
replace instrument cluster circuit board. If scan tool displays BUS
SHORT TO GROUND, go to next step.
4) Turn ignition off. Disconnect compass mini-trip computer.
Turn ignition on. If scan tool does not display BUS SHORT TO GROUND,
replace compass mini-trip computer. If scan tool displays BUS SHORT TO
GROUND, go to next step.
5) Turn ignition off. Disconnect CCD radio. Turn ignition on.
If scan tool does not display BUS SHORT TO GROUND, replace radio. If
scan tool displays BUS SHORT TO GROUND, go to next step.
6) Turn ignition off and wait 2 minutes. Disconnect Air Bag
Control Module (ACM). ACM is located under center of instrument panel.\
Turn ignition on. If scan tool does not display BUS SHORT TO GROUND,
replace ACM. If scan tool displays BUS SHORT TO GROUND, go to next
step.
7) Turn ignition off. Disconnect Central Timer Module (CTM).\
CTM is located under left side of instrument panel. Turn ignition on.
If scan tool does not display BUS SHORT TO GROUND, replace CTM. If
scan tool displays BUS SHORT TO GROUND, go to next step.
8) Disconnect scan tool from DLC. Using external ohmmeter,
measure resistance between ground and DLC connector terminal No. 3
(Violet/Brown wire). If resistance is less than 700 ohms, repair
Violet/Brown wire for short to ground. If resistance is 700 ohms or

full load. The Kent-Moore J-39021 is such a tool, though there are
others. The Kent-Moore costs around $240 at the time of this writing
and works on many different manufacturer's systems.
The second method is to use a lab scope. Remember, a lab
scope allows you to see the regular operation of a circuit in real
time. If an injector is having an short or intermittent short, the lab
scope will show it.
Checking Available Voltage At the Injector
Verifying a fuel injector has the proper voltage to operate
correctly is good diagnostic technique. Finding an open circuit on the
feed circuit like a broken wire or connector is an accurate check with
a DVOM. Unfortunately, finding an intermittent or excessive resistance
problem with a DVOM is unreliable.
Let's explore this drawback. Remember that a voltage drop due
to excessive resistance will only occur when a circuit is operating?
Since the injector circuit is only operating for a few milliseconds at
a time, a DVOM will only see a potential fault for a few milliseconds.
The remaining 90+% of the time the unloaded injector circuit will show
normal battery voltage.
Since DVOMs update their display roughly two to five times a
second, all measurements in between are averaged. Because a potential
voltage drop is visible for such a small amount of time, it gets
"averaged out", causing you to miss it.
Only a DVOM that has a "min-max" function that checks EVERY
MILLISECOND will catch this fault consistently (if used in that mode).\
The Fluke 87 among others has this capability.
A "min-max" DVOM with a lower frequency of checking (100
millisecond) can miss the fault because it will probably check when
the injector is not on. This is especially true with current
controlled driver circuits. The Fluke 88, among others fall into this
category.
Outside of using a Fluke 87 (or equivalent) in the 1 mS "min-\
max" mode, the only way to catch a voltage drop fault is with a lab
scope. You will be able to see a voltage drop as it happens.
One final note. It is important to be aware that an injector
circuit with a solenoid resistor will always show a voltage drop when
the circuit is energized. This is somewhat obvious and normal; it is a
designed-in voltage drop. What can be unexpected is what we already
covered--a voltage drop disappears when the circuit is unloaded. The
unloaded injector circuit will show normal battery voltage at the
injector. Remember this and do not get confused.
Checking Injector On-Time With Built-In Function
Several DVOMs have a feature that allows them to measure
injector on-time (mS pulse width). While they are accurate and fast to\
hookup, they have three limitations you should be aware of:
* They only work on voltage controlled injector drivers (e.g
"Saturated Switch"), NOT on current controlled injector
drivers (e.g. "Peak & Hold").
* A few unusual conditions can cause inaccurate readings.
* Varying engine speeds can result in inaccurate readings.
Regarding the first limitation, DVOMs need a well-defined
injector pulse in order to determine when the injector turns ON and
OFF. Voltage controlled drivers provide this because of their simple
switch-like operation. They completely close the circuit for the
entire duration of the pulse. This is easy for the DVOM to interpret.
The other type of driver, the current controlled type, start
off well by completely closing the circuit (until the injector pintle
opens), but then they throttle back the voltage/current for the
duration of the pulse. The DVOM understands the beginning of the pulse

but it cannot figure out the throttling action. In other words, it
cannot distinguish the throttling from an open circuit (de-energized)
condition.
Yet current controlled injectors will still yield a
millisecond on-time reading on these DVOMs. You will find it is also
always the same, regardless of the operating conditions. This is
because it is only measuring the initial completely-closed circuit on-
time, which always takes the same amount of time (to lift the injector
pintle off its seat). So even though you get a reading, it is useless.
The second limitation is that a few erratic conditions can
cause inaccurate readings. This is because of a DVOM's slow display
rate; roughly two to five times a second. As we covered earlier,
measurements in between display updates get averaged. So conditions
like skipped injector pulses or intermittent long/short injector
pulses tend to get "averaged out", which will cause you to miss
important details.
The last limitation is that varying engine speeds can result
in inaccurate readings. This is caused by the quickly shifting
injector on-time as the engine load varies, or the RPM moves from a
state of acceleration to stabilization, or similar situations. It too
is caused by the averaging of all measurements in between DVOM display
periods. You can avoid this by checking on-time when there are no RPM
or load changes.
A lab scope allows you to overcome each one of these
limitations.
Checking Injector On-Time With Dwell Or Duty
If no tool is available to directly measure injector
millisecond on-time measurement, some techs use a simple DVOM dwell or
duty cycle functions as a replacement.
While this is an approach of last resort, it does provide
benefits. We will discuss the strengths and weaknesses in a moment,
but first we will look at how a duty cycle meter and dwell meter work.
How A Duty Cycle Meter and Dwell Meter Work
All readings are obtained by comparing how long something has
been OFF to how long it has been ON in a fixed time period. A dwell
meter and duty cycle meter actually come up with the same answers
using different scales. You can convert freely between them. See
RELATIONSHIP BETWEEN DWELL & DUTY CYCLE READINGS TABLE .
The DVOM display updates roughly one time a second, although
some DVOMs can be a little faster or slower. All measurements during
this update period are tallied inside the DVOM as ON time or OFF time,
and then the total ratio is displayed as either a percentage (duty
cycle) or degrees (dwell meter).
For example, let's say a DVOM had an update rate of exactly 1
second (1000 milliseconds). Let's also say that it has been
measuring/tallying an injector circuit that had been ON a total of 250
mS out of the 1000 mS. That is a ratio of one-quarter, which would be
displayed as 25% duty cycle or 15
dwell (six-cylinder scale). Note
that most duty cycle meters can reverse the readings by selecting the
positive or negative slope to trigger on. If this reading were
reversed, a duty cycle meter would display 75%.
Strengths of Dwell/Duty Meter
The obvious strength of a dwell/duty meter is that you can
compare injector on-time against a known-good reading. This is the
only practical way to use a dwell/duty meter, but requires you to have
known-good values to compare against.
Another strength is that you can roughly convert injector mS
on-time into dwell reading with some computations.
A final strength is that because the meter averages
everything together it does not miss anything (though this is also a