No-Start Diagnosis
The diagnostic
procedure for EI (electronic ignition)
systems varies depending on the vehicle make
and model year. Always follow the procedure
recommended in the vehicle manufacturer's
service manual.
The following
procedure is based on Chrysler EI systems.
The crankshaft timing sensor and camshaft
reference sensor in these systems are
modified Hall-effect switches.
If a crank or cam
sensor fails, the engine will not start.
Both of these sensor circuits can be checked
with a voltmeter
or lab scope.
If the sensors are
receiving the correct amount of voltage and
have good low-resistance ground circuits,
their output should be a pulsing digital
signal or voltmeter reading while the engine
is cranking.
If any of these
conditions do not exist, the circuit needs
to be repaired or the sensor needs to be
replaced. When the engine fails to start,
follow these steps:
- Check for fault
codes 11 and 43.
- Code 11,
"Ignition Reference
Signal," could be caused by a
defective camshaft reference signal
or crankshaft timing sensor signal.
- Code 43 is
caused by low primary current in
coil number 1, 2 or 3.
- With the engine
cranking, check the voltage from the
orange wire to ground on the crankshaft
timing sensor and the camshaft reference
sensor.
Crankshaft
timing and camshaft reference sensor
terminals.
- Over 7V is
satisfactory.
- If the voltage
is less than specified, repeat the
test with the voltmeter connected
from PCM (powertrain control module)
terminal 7 to ground.
- If the voltage
is satisfactory at terminal 7 but
low at the sensor orange wire,
repair the open circuit or high
resistance in the orange wire.
- If the voltage
is low at terminal 7, the PCM may
need replacement.
- Be sure 12V
are supplied to the PCM terminal
3 with the ignition switch off
or on, and 12 V must be supplied
to PCM terminal 9 with the
ignition switch on.
- Check PCM
ground connections on terminals
11 and 12 before PCM
replacement.
- With the ignition
switch on, check the voltage drop across
the ground circuit (black/light blue
wire) on the crankshaft timing sensor
and the camshaft reference sensor.
- A reading below
0.2V is satisfactory.
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When using a digital voltmeter to
check a crankshaft or camshaft
sensor signal, crank the engine a
very small amount at a time and
observe the voltmeter. The voltmeter
reading should cycle from almost 0
volts to a highter voltage of about
5 volts. Since digital voltmeters do
not react instantly, it is difficult
to see the change in voltmeter
reading if the engine is cranked
continually.
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- If the readings in
the previous two steps are satisfactory,
connect a lab scope or digital voltmeter
from the gray/black wire on the
crankshaft timing sensor and the
tan/yellow wire on the camshaft
reference sensor to ground.
Lab scope
patterns from the camshaft and
crankshaft position sensors.
- When the engine
is cranking, a digital pattern
should be displayed or the voltmeter
should cycle between 0 and 5 volts.
- If the voltage
does not cycle, sensor replacement
is required.
- Each sensor
voltage signal should cycle from low
voltage to high voltage as the
engine is cranked.
A no-start condition
can occur if the PCM "locks up."
- In step 2 above, if
0 volts is indicated the PCM may be
faulty or it may be locked up.
- If the PCM is
locked up it will not store a fault code
for the reason.
- Basically, the PCM
will lock up when it goes into a
safeguard routine if the 9-volt or
5-volt reference voltage shorts to
ground. This shuts down the PCM to
protect it. Since it shuts down, no DTCs
(Diagnostic trouble code) are stored.
- The engine will not
start as long as the ground is present.
An intermittent ground will cause the
engine to stop running.
- Attempting to
restart the engine without cycling the
ignition switch to the full LOCK
position will not start the engine, even
if the ground is lifted.
- Cycle the
ignition switch to the LOCK position
and wait about 5 to 10 seconds.
- If the ground
is lifted, the PCM will reset and
the engine will start and run until
the ground occurs again.
- On 1996 and new
SBEC III and JTEC engine controllers,
there are two 5-volt reference signals.
The sensors that require 5 volts are
separated, thus If this signal shorts to
ground the engine will still stop
running, but for the first time a DTC
can be set.
- Also note, if the
9-volt reference voltage is opened,
there will be no DTC stored for the
crankshaft or camshaft positions
sensors. With an open circuit the PCM
cannot tell if the engine is cranking or
not. The diagnostic routing does not
begin until the PCM senses engine
cranking.
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