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Coolant temperature sensor issues

VB242

VB242

I.M. Weasel
Joined
Sep 21, 2011
Location
Driving the No Malarkey Bus
I've been fighting some crazy clt readings. First they were super sketchy, spikes to 240F all the way to -26F. I changed out the parts store sensor with a Bosch (lh2.2 blue that grounds through 1 of the the wires) I had. It worked properly for a couple days then back to derpville. I was checking for continuity and opened up the pins on the microsquirt connector, so pulled out the pins and made them round again with some wire strippers and reinstalled. The gauge on tuner studio reads 180F constantly no matter if the sensor is connected if I short it with a piece of wire, nothing seems to change the reading. I do have 4.95 volts at the connector with the engine running. I also checked continuity in from the engine side connector to where the wires splice into the microsquirt loom. I'm at a loss, unless it's still not making a good connection to the microsquirt. Is there a setting that says to ignore the clt sensor somewhere that I inadvertantly clicked? I've also reloaded the firmware. What else can I check/do/test? Also reading the Bosch data sheet on the sensor it says it needs a pull-up resistor, but I've been running over a year without one. Is that what the bias resistor setting on the clt calibration page is for? Not clear in the documentation. I've also tried changing the polarity of the sensor wiring.
 
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Do you have a simulator? plug that in to the microsquirt, turn the CLT dial and at least you can figure out if the problem is in the ECU or in the harness/engine. I don't think there are any settings to click that would turn off the coolant sensor.

The bias resistors and pull up resistors are built in to the microsquirt board. Nothing external is needed. The bias resistor isn't perfect for the Volvo bosch sensor. I think they are calibrated for GM CLT sensors out of the box. But they work fine regardless.
 
I don't have a simulator since microsquirt is put together sealed. I will recheck the pin in the amp seal connector, maybe it's making enough contact to pass voltage for the vom but not enough current for the processor to read? I had to wiggle the amp seal to get tuner studio to connect.
 
Again I checked for a resistance reading and got normal values at the pins on the amp seal connector. I test drove it and datalogged it and only had 180F max and min for the whole trip. On the return from pick and pull, I cut the yellow coolant sensor wire and had some variation 193F-123F but only in spikes. I'm thinking there's something wrong with the microsquirt. Any other ideas?
 
Update, I set the bias resistor setting to 2490 not 2.490 perhaps I saw 2,490 on that field. Anyway the gauge in tuner studio started working again, I didn't get much log time to see if there was any spiking happening. I will update after this weekend's festivities.
 
filter the clt signal, but also double check your grounds and run your sensor grounds to a common location with the MS.

it will also probably pop a failsafe value if it's not getting a signal, so you could have a continuity issue that's somewhat intermittent.
 
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