Document 229539

his is another interesting
vehicle, an automatic
which came in with
check engine light on,
emission light on, intermittent
miss and no power.
First I scanned for fault codes
and got these:
P0700 EOBD error stored by
transmission control module
P0335 crankshaft sensor open
P0336 crankshaft sensor
incorrect signal
P1700 not present SVS request
via can
P0725 not present no engine
speed information
P1895 not present actual
torque circuit fault
Armed with this information
and remembering one of Nick
Murphy’s articles on diagnostics,
Astra 2004
A sensor signal
SAI ! with high
I started at the crank angle
sensor. After hooking up the pico
I found a signal I did not expect to
see (pic 1).
I increased the RPM and sort of
got something a bit better (pic 2).
I still was not really happy with it
so being new to the scope world
I made a quick call to someone
who uses a scope regularly and
he said that unless you have a
good sample to check against, it
can be difficult. I knew from pic 1
that we had a problem.
If the pattern looked OK at the
sensor, I was going to recheck
it at the engine control unit
(ECU) just in case it was a wiring
problem. I removed the sensor
and checked its resistance which,
it seemed, was open circuit. I
was pretty sure it should have a
resistance value (pic 3).
Then I decided to check the
sensor against a new and
genuine item from my EFI
supplier, and it did have a circuit
(pic 4). That was good enough
for me because I did not want to
be stuck with a part that did not
fix the car.
I rechecked on the scope – a
picture tells a thousand words
(pic 5). The signal on the scope
was now what I was expecting
to see.
When I tried to clear the codes
in the ECU with the Tech 2, I had
to clear the transmission control
module first before the ECU
codes would clear.
I also noticed with the old sensor
it took a second longer to start
than what you would expect. With
the new sensor, it seemed much
better. Then I gave it a decent
road test, with some stop/starts –
around the block just doesn’t cut
it anymore. A final check with the
scan tool and all was OK. We
were left with a happy Astra and
a happier customer.
Peter Hinds
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