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Engine coolant temp sensor 700 1990

posted by  Brick Skinner on  Mon Aug 12 06:22 CST 2013
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last visit: Fri Jun 13 13:31 CST 2014
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Recovering from a blown head gasket and overheat. Many new components under the hood including a new ECT sensor (the one that's hard to get to). The engine starts and runs just fine except that the CEL comes on within seconds of starting and throwing a 1-2-3 code. The computer will reset but the fault comes right back. The sensor and connector are verified to be the correct ones and bench test good and the wiring has been traced back to the control units. All good.

This is really driving me crazy. The guy who helps me he most gets the cookie!
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    SOLVED - Engine coolant temp sensor 700 1990

    posted by  Brick Skinner on  Fri Aug 16 12:06 CST 2013
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    I get the cookie.

    Problem was the wrong sensor. Brand new but still wrong.

    TIP: When your ECT sensor goes bad, don't opt for the cheaper AutoZone brand. Find the OEM Bosch unit or go to Advance Auto for a suitable alternative. The correct one is hard to find and much more costly but its the only way.

    The AZ unit has a blue connector while the correct ones have a black connector. Apparently there are two NTC thermistors crammed into the sensor that provide data to the LH Jetronic and Ignition computers respectively.

    Happy days!
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      SOLVED - Engine coolant temp sensor 700 1990

      uid 55's pic
      posted by  john sargent on  Sat Aug 17 08:06 CST 2013
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      LH 2.2 and LH 2.4 use different Engine Coolant Temperature sensors.

      Yes, LH 2.4 has two thermistors, one for the ECU (fuel computer), and one for the EZK (ignition computer). They internally grounded.

      LH 2.2 has one thermistor (for the fuel computer), externally grounded on the intake manifold.

      You had a sensor for LH 2.2 installed on LH 2.4. That doesn't work, but an LH 2.4 sensor does work on LH 2.2
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      john








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      SOLVED - Engine coolant temp sensor 700 1990

      posted by  Chris Mullet on  Fri Aug 16 23:32 CST 2013
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      I have found you have to be real careful buying parts from the big chain parts houses. They're OK for some things like brake pads, but when it comes to something like coolant temp sensors their catalogue will list a part but it's often suspect.








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    Engine coolant temp sensor 700 1990

    uid 55's pic
    posted by  john sargent on  Tue Aug 13 07:15 CST 2013
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    The Knock Sensor connector and the Engine Coolant Sensor have electrical connectors that will interchange. You wouldn't be the first person to interchange them. Check them very closely.
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    john








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      Engine coolant temp sensor 700 1990

      posted by  Chris Mullet on  Tue Aug 13 08:45 CST 2013
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      "...The Knock Sensor connector and the Engine Coolant Sensor have electrical connectors that will interchange..."

      That's it! (I was thinking the cold start injector was the confused component.) If everything is right with the world, I believe the wire colors should be:

      ECT sensor for Regina system - Gray/White and Red/Black
      Knock sensor - Black and Green
      Cold Start injector - Gray/Black and Blue/Green
      Temp Sensor for Gauge - Yellow/Black and Yellow/White

      This is according to a wiring diagram I found online.








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    Engine coolant temp sensor 700 1990

    posted by  Brick Skinner on  Mon Aug 12 20:49 CST 2013
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    I found some Regina info on line that says ECT is used by the control unit to calculate injection timing during warm-up. Voltage across sensor should be 0.3V for hot engine and 2.0V for cold. Voltage increases when engine is cold.

    I just now verified that my sensor matches these spec's. Still getting a CEL.
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    Engine coolant temp sensor 700 1990

    posted by  aleekat on  Mon Aug 12 07:38 CST 2013
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    I know you stated "correct one". Blue or black sensor? Have you verified the connector pins have not pushed back?
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    Engine coolant temp sensor 700 1990

    posted by  JimSig on  Mon Aug 12 06:38 CST 2013
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    Are you sure the right connector is attached to the sensor? If I remeber correctly the connector is the same as the throttle position switch - or maybe it's the IAC that uses the same connector - can't remember which for sure but it isn't hard to get them reversed.








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      Engine coolant temp sensor 700 1990

      posted by  Brick Skinner on  Mon Aug 12 06:41 CST 2013
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      Verified. That actually did cross my mind but I think the one that people have trouble with is swapping the IAC and TPS plugs.
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        Make it a chocolate chip cookie (maybe??) 700 1990

        posted by  Chris Mullet on  Mon Aug 12 13:16 CST 2013
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        I'm straining my memory, but I want to say the ECT and cold start injector (both two-pin connectors) are interchangeable. And they're both right there in the same neighborhood - easily confused. If you have a Regina with the cold start mod, you would be getting a cold start injector fault code regardless of whether you have the wires mixed up or not. But if the wires WERE mixed up, the ECT sensor fault code would be added to equation.








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          Gauge senser and ECT ? 700 1990

          uid 49372's pic
          posted by  740_dan on  Mon Aug 12 14:51 CST 2013
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          I thought it was the coolant *gauge* sensor and ECT have same connector. Both connect into head on same side inches apart.
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            Gauge senser and ECT ? 700 1990

            posted by  Brick Skinner on  Mon Aug 12 17:02 CST 2013
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            coolant gauge sensor and ECT sensor have different connectors but they work the same. I jury rigged a swap and got the same results. Both sensors test good.
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