2005 XG 350 Check engine light
#1
2005 XG 350 Check engine light
My check engine light came on today at the same time my tachometer went out down to zero and has stayed there, so I guess it's broke. I guess my question would be is the tachometer going out what caused the light to come on?
#4
Wait, the knock sensor drives the Tach??
Never heard of this.
Thought it was the crankshaft sensor or may be the camshaft sensor (although I don't think it is so) that gives the ECU the info on engine rpm and thus the tach.
Never heard of this.
Thought it was the crankshaft sensor or may be the camshaft sensor (although I don't think it is so) that gives the ECU the info on engine rpm and thus the tach.
#5
Sorry, my bad (shooting from the hip ...)
What I actually meant is the ignition failure sensor.
Of course the tach signal comes from the engine ECU but the signal source used to create the tach signal is the ignition, not cam or crank sensors.
When your rev counter/tach isn't working and you have CEL/MIL on, very likely you can see
P0320 Ignition failure sensor open/short
stored.
What I actually meant is the ignition failure sensor.
Of course the tach signal comes from the engine ECU but the signal source used to create the tach signal is the ignition, not cam or crank sensors.
When your rev counter/tach isn't working and you have CEL/MIL on, very likely you can see
P0320 Ignition failure sensor open/short
stored.
#7
+12V get supplied thru ign.fail.sensor to coils. PCM pulls coils to GND for spark (via power transistor in coil head). Ign.fail.sensor monitors 12V line current pulsating and outputs this to tach (trigger circuitry generating square 'wave') and via wire splice back into PCM. This way PCM can trigger CEL/MIL.
I haven't invented this, I can just read circuit diagrams ... (and by that I have to correct myself up there: tach signal doesn't come from/thru PCM but from sensor directly. Still the result is the same: Broken tach in most cases means broken ign.fail.sensor)
I haven't invented this, I can just read circuit diagrams ... (and by that I have to correct myself up there: tach signal doesn't come from/thru PCM but from sensor directly. Still the result is the same: Broken tach in most cases means broken ign.fail.sensor)
Last edited by e3tom; 01-27-2016 at 03:56 AM.
#8
From your diagram, when the signal from the ECM goes high then the transistor is pulled down and the collapsing magnetic field in the coil then causes the spark to jump across the spark plugs.
The pulling down to GND is then seen by the Op amp in the Ignition failure sensor whose output then drives the base of the transistor high and the collector to go low
This signal feeds both the ECM and the Tach on the instrument cluster
But the ECM doesn't know when to fire the coils unless there is another sensor telling the ECM when it is the right time to fire the spark plugs
So even though the ignition failure sensor is connected to the tach on the dash, there is another sensor as well as the ECM that can also give similar symptoms of a failed tach
It needs a little more testing to be sure
Edit: Is the engine still running? Or has it stopped?
The pulling down to GND is then seen by the Op amp in the Ignition failure sensor whose output then drives the base of the transistor high and the collector to go low
This signal feeds both the ECM and the Tach on the instrument cluster
But the ECM doesn't know when to fire the coils unless there is another sensor telling the ECM when it is the right time to fire the spark plugs
So even though the ignition failure sensor is connected to the tach on the dash, there is another sensor as well as the ECM that can also give similar symptoms of a failed tach
It needs a little more testing to be sure
Edit: Is the engine still running? Or has it stopped?
Last edited by avisitor; 01-28-2016 at 12:54 AM.
#9
spark timing is determined by cam & crank sensors, ign.fail.sensor provides 'ignition success' feedback to ECM and drives tach.
What is to be discussed about that ? When engine runs fine and all that fails is the tach what else than ign.fail.sensor is the prime suspect (and it is known to fail ...) ???
Easy to diagnose, too. Read codes, get P0320, wham !
Or put piece of wire instead of sensor (read the appropriate pins from the schematic) to feed coils and if nothing changes and engine still runs the same way as before ...
Maybe one day the OP will report back here. Until then, I'm out.
What is to be discussed about that ? When engine runs fine and all that fails is the tach what else than ign.fail.sensor is the prime suspect (and it is known to fail ...) ???
Easy to diagnose, too. Read codes, get P0320, wham !
Or put piece of wire instead of sensor (read the appropriate pins from the schematic) to feed coils and if nothing changes and engine still runs the same way as before ...
Maybe one day the OP will report back here. Until then, I'm out.