coolant sensor

ok 1988 buick lesabre got a 15 code meaning coolant sensor or cicuit/low temperature indicated. replaced the coolant sensor with new one and removed my negative battery cable to reset the codes. a few weeks later my service
engine light came on and i got the same code reading. the engine has been hard to start also during this time . where should i go from here.
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scratch wrote:

There could be an intermittent connection in the wiring going to that same sensor. Otherwise, it could be the quad driver circuit in the computer where that wiring hooks in.
---Bob Gross---
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First, do you know how to enter/use the diagnostics? If so, check the coolant temp(C) value, P.0.4. If the value reads -40 to -35>check the connection on the new sensor connector for any kind of crud/dirt/etc. Jiggle the yellow and blk/wht wires around while watching the parameter value. If the value changes while you are doing this, there is a faulty connection in that circuit. The yellow wire is Ckt410.....it is the wire to the ECM. The blk/wht wire(Ckt476) is a common ground for the sensor and the TPS to the ECM. Check out all those connections and connectors. With a new sensor, the most likely cause is a wiring-type problem.
E15 is set because the ECM assumes the coolant temp can't be -35C or less and the MAT sensor is 5C or greater; (E15= sensor signal is open to sensor)
Check the MAT sensor circuit also.
Before you disconnected the power were there any other codes?
BTW: disconnecting the power to clear any codes isn't a good thing to do. What that does is clear the RAM which contains data to help the ECM/BCM maintain the best it can to cope with 'less than new' components in the systems. When the power is cut to the computer, everything reverts to the default programs.....when every sensor/etc. was brand new and functioning as so. I suspect this is why the car has been difficult to start. Eventually the computer will 'relearn' and compensate.
Hope this is of some use......
Dave S(Texas)
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no i do not know how to enter/use the diagnostics. i have been able to check everything so far on this car with my voltmeter.

First, do you know how to enter/use the diagnostics? If so, check the coolant temp(C) value, P.0.4. If the value reads -40 to -35>check the connection on the new sensor connector for any kind of crud/dirt/etc. Jiggle the yellow and blk/wht wires around while watching the parameter value. If the value changes while you are doing this, there is a faulty connection in that circuit. The yellow wire is Ckt410.....it is the wire to the ECM. The blk/wht wire(Ckt476) is a common ground for the sensor and the TPS to the ECM. Check out all those connections and connectors. With a new sensor, the most likely cause is a wiring-type problem.
E15 is set because the ECM assumes the coolant temp can't be -35C or less and the MAT sensor is 5C or greater; (E15= sensor signal is open to sensor)
Check the MAT sensor circuit also.
Before you disconnected the power were there any other codes?
BTW: disconnecting the power to clear any codes isn't a good thing to do. What that does is clear the RAM which contains data to help the ECM/BCM maintain the best it can to cope with 'less than new' components in the systems. When the power is cut to the computer, everything reverts to the default programs.....when every sensor/etc. was brand new and functioning as so. I suspect this is why the car has been difficult to start. Eventually the computer will 'relearn' and compensate.
Hope this is of some use......
Dave S(Texas)
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