Re: bad coolant sensor flashes on the information display
Take it back to the dealer and then have them check the computer to see if something else comes up. But this is not right that they did not solve the problem. Insist that you get some concrete service and a better answer. The '90's were not the best years for the Grands and there were recalls. The VIN should be checked to see is there were prior recalls.
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Corrosion in electrical connections causes some bad behaviors. Usually there is a critical temp sensor that provides block temp information to the ECU. It usually has a two or three wire connection to the sensor. And a difficult to remove connector. My 20yr old (other make) gave me a bout of teriable starting when cold. I found this "special sensor" (some people say the sensor needs to be changed. I found that cleaning to bright metal provided the needed almost like new start without needing to replace the sensor. On mine there is a second "simple" temp sensor one wire to the dashboard temp display. Hope this helps.
This sounds like a bad coolant temp sensor that give computer false reading, check the coolant temp sensor connector and if it is good with no bad wires to connector then replace coolant temp sensor , when the computer gets a signal from temp sensor that engine is hot it turns fans on high speed to cool radiator and displays a/c turned off , if this truck does not have electric cooling fans then they wont run just explaining what happens depending on engine and cooling set up. replace coolant temp sensor and check connector.
Check out a new coolant sensor. Some vehicles have 2 and one works the dash gauge and the other is needed for Engine management(Fuel mix, timing). Ask at Autozone or go to Advance, or Oreilys for a second scan.
The O2 sensors control how the engine runs. Sometimes they will self-clean, but if you have a bad indication, they should be changed. I usually work on Ford brands but this is pretty universal. The scanners should also tell you which O2 is bad out of the many you may have on your car.
A code P0010 may mean that one or more of the following has happened:
Faulty oil control valve (OCV)
Open or short in the VVT/VCT circuit
Open or short in the OCV / solenoid valve
Damaged computer (PCM)
Some recommended troubleshooting and repair steps are:
Carefully inspect the Bank 1 VVT/VCT system circuit wiring and connectors, repair as required
With a warm engine, test the operation of the OCV, replace/repair as needed
A code P0128 may mean that one or more of the following has happened:
Low engine coolant level
Leaking or stuck open thermostat
Faulty cooling fan (running too much)
Faulty coolant temperature sensor ECT
Faulty intake air temperature (IAT) sensor
Past experience indicates that the most likely solution is to replace the thermostat.
However here are some suggestions on troubleshooting and repairing a P0128 OBD-II
Verify coolant strength & level
Verify proper cooling fan operation (check if it's running more than it
should). Replace if necessary.
Verify proper engine coolant temperature (ECT) sensor operation, replace
Verify proper intake air temperature (IAT) sensor operation, replace if
If the above items check out good, replace the thermostat
P0641 is a generic code for a possible bad ECU. I would first fix the other two issues and then clear the check engine light and see if it comes back on. If it does, then you have a possible bad ECU and will need to run further tests to see if that is the case or not
check that the EGR valve is not sticking or has a vacuum leak. This valve will not operate until the engine is warm.
check also the engine coolant temp sensor (ECT). This sensor tells the engine computer that the engine has warmed up, so if it is faulty, it could be sending wrong information to the computer. If the sensor is disconnected, wires to it broken, or faulty in full cold mode, it will tell the computer that the engine is very cold, like -40F. The computer will schedule fuel for cold conditions. This is usually way too much fuel for a warm engine and it will rich misfire, idle rough, and be difficult to start warm.
The ECT has two wires going to it and is dedicated to sending information to the engine computer. It has nothing to do with your dash gauge that shows coolant temp. That sender has only one wire and is dedicated to the coolant temp gauge.
What repair did you make when the "bad coolant sensor" light came on? If you did nothing, I'm sure you know that not only does the sensor give you temperature info, it also tells the computer when the engine is warmed up so it can properly manage fuel delivery. That same information tells the computer when to turn any auxiliary electric fans on, or to modify the engine timing to cool down the engine. At this point your only best option is to replace the sensor, the thermostat and re-fill with the proper mix of coolant. Check everything over for leaks and hope you have not sustained any major internal engine damage (head gaskets or cracked heads). Good luck!!
The Engine Coolant Temperature (ECT) sensor is mounted in the intake manifold and sends engine temperature information to the ECM. The ECM supplies 5 volts to the coolant temperature sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage which it interprets as a cold engine. As the sensor warms (internal resistance low), the ECM monitors a low signal voltage which it interprets as warm engine. Fig. 1: View of the Engine Coolant Temperature (ECT) sensorFig. 2: Engine Coolant Temperature (ECT) sensor locationTESTING
See Figures 3 and 4
Remove the ECT sensor from the vehicle.
Immerse the tip of the sensor in container of water.
Connect a digital ohmmeter to the two terminals of the sensor.
Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the engine coolant sensor temperature vs. resistance illustration.
Repeat the test at two other temperature points, heating or cooling the water as necessary.
If the sensor does not meet specification, it must be replaced.
Fig. 3: Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensor wiring diagramFig. 4: ECT sensor temperature vs. resistance values