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Old 02-10-2005, 09:47 PM   #1
plumsl2
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Default Lessons in ECT sensors

I was recently inspired to write this because for some reason people thing the ECT is always the problem around here.

Lets talk about the speed density vehicle, which most saturns are. During start-up there is only 1 critical input sensor: the ECT. When you turn the key to the start position the computer looks at the ECT to determine how much fuel is needed to start that car (because the temperature of the coolant is very close to the outside air temperature). After the car is started, the ECT becomes a secondary sensor, now there are 3 primary sensors to determine fuel: IAT(intake air temp sensor), MAP(manifold absolute pressure), TPS throttle position sensor). The computer looks at these 3 sensors to determine the pulse width of the injectors so the car can run. For example, cruising down the road the computer sees the TPS is at x%, the MAP is showing X amount of vacuum and the IAT is reading X degrees, so therefore the computer is going to put X amount of fuel into the engine for it to run. When an ECT sensor goes bad you can get problems like bad gas milege, lean misfire, no start, poor performance.

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Old 02-10-2005, 10:01 PM   #2
Razorbak
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1996 SL2
Default Re: Lessons in ECT sensors

Quote:
Originally Posted by plumsl2
I was recently inspired to write this because for some reason people thing the ECT is always the problem around here.
I think it has more to do with the simple fact that, of the three sensors that you mentioned (ECT, MAP, TPS), the pre-2001 ECT sensor had a known design flaw, was redesigned by Saturn, and is covered under a TSB recommending it's replacement under certain conditions. Known failure points tend to get a lot of focus from people attempting to troubleshoot problems. Think of it as mechanical profiling.

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Old 02-11-2005, 08:41 AM   #3
Amp67
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Default Re: Lessons in ECT sensors

Actually, engine speed and manifold pressure are the primary inputs to compute airflow in a speed density system. The IAT provides an ideal gas law density correction to account for changes in ambient temperature. Also, the barometric pressure is determined (at key up from MAP and during operation). Altitude also impacts the airflow calculation. TPS is used for other things (like assessing driver intent). TPS input does not go into the airflow calculation unless MAP sensor fails. Once airflow is determined, the engine is fueled to this airflow and whatever AFR is commanded. At stoich, the O2 sensor is able to provide the PCM with feedback that ultimately impacts fuel pulsewidth adjustment. Engine wear changes that impact volumetric efficiency, like reduced cam lobe profile, will cause the airflow calculation to be off. Subsequently, the necessary O2 feedback corrections can be made at stoich to compensate for this wear.

Sorry for being anal about the details...

Amp

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Old 02-11-2005, 11:13 AM   #4
Luke
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Default Closed vs Open Loop operation

And with the exceptionally well detailed discussion above, I'll just add:

The PCM (Powertrain Control Module) operates in two different fuel control modes. Open-Loop and Closed-Loop. Whenver the vehicle is first started, the PCM operates in Open-Loop fuel control. When the PCM determines that the engine coolant temperature (ECT) sensor has reached atleast 68 degrees F, and the oxygen sensor has reached operating temperature of 600 degrees F, the PCM will then go into Closed-Loop fuel control opertions.

If there are any oxygen sensor related PCM/EC diagnostic trouble codes, or if the oxygen sensor does not switch between rich and lean, or if the ECT does not obain 68 degrres F, the PCM will not go into Closed Loop fuel control operation. In Open Loop fuel control, the air/fuel mixture is pre-determined by the PCM's already installed program. *

My understanding is that while in Open-Loop, upon the engine's initial start-up, the operating parameters are constant, pre-set, and do not change while in Open-Loop status.

* Source= FSM (Factory Service Manual) Engine Electronic Controls
Page 23.

...
> 95 SL 2 = 653,369 Miles 40.4 MPG, as of 5/20/11. My manual Radiator Fan Switch, courtesy of Wolfman's patient installation guidance, continues to be.......invaluable < The car was retired

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Old 02-11-2005, 09:59 PM   #5
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Default Re: Lessons in ECT sensors

Quote:
Originally Posted by Razorbak
the pre-2001 ECT sensor had a known design flaw, was redesigned by Saturn, and is covered under a TSB recommending it's replacement under certain conditions.
Technical Service Bulletins - Customer Interest

Engine - Driveability Concerns/Cooling System DTC's Set

BULLETIN: 01-T-07

ISSUE DATE: February, 2001

CATEGORY TYPE: Engine-03

CATEGORY: Emission Controls

CORPORATION NO.: 01-06-04-005

SUBJECT:

Engine Coolant Temperature Sensor Related Diagnostic Trouble Code(s) and/or the Following Conditions: Hard Start, Erratic Idle, Rough Running. Engine Overheating, Low and/or Leaking Coolant, and/or Service Engine Soon Lamp Illuminated. (Replace Engine Coolant Temperature Sensor with New Design Sensor- P/N 21025106)

MODELS AFFECTED:

1991-2001 Saturn S-Series vehicles

CONDITION:

Customers may comment about various driveability and/or engine operating concerns including: hard start, erratic idle, rough running, engine overheating, low and/or leaking coolant, and/or Service Engine Soon lamp illuminated.

CAUSE:

This condition may be caused by a cracked engine coolant temperature sensor.

CORRECTION:

Replace engine coolant temperature sensor, inspect and if necessary replace sensor harness connector. Refer to procedure in this bulletin to replace engine coolant temperature sensor and Parts Requirements for specific parts information.

PROCEDURE

1. Disconnect engine coolant temperature sensor electrical connector and inspect sensor and connector terminals for corrosion and/or evidence of engine coolant.

^ If terminals are corroded or if there is evidence of engine coolant proceed to step 4.

^ If terminals are not corroded and there is no evidence of engine coolant, reconnect the electrical connector and continue to next step.

CAUTION: TO AVOID THE DANGER OF BEING BURNED, DO NOT REMOVE THE CAP WHILE THE ENGINE, RADIATOR, AND SURGE TANK ARE STILL HOT. SCALDING FLUID AND STEAM CAN BE BLOWN OUT UNDER PRESSURE.

2. Perform one or both of the following checks to determine whether the engine coolant temperature sensor is providing the correct temperature indication.

^ If engine is at ambient temperature (vehicle has been sitting overnight or not started for several hours), use a Scan tool to compare the inlet air temperature (IAT) to the engine coolant temperature (ECT). These two readings should be within 2C (4F) of each other.

^ If engine is at operating temperature, install a thermometer in the coolant recovery reservoir. With the engine running and A/C off, use a Scan tool to compare the engine coolant temperature sensor reading to the thermometer reading. These two readings should be within 8C (15F) of each other.

If engine coolant temperature sensor reading does not pass either of the above tests, continue with next step.

If engine coolant temperature sensor reading passes both of the tests above, refer to appropriate symptom diagnostic chart in the Engine/Emissions Controls Section of applicable Engine Service Manual.
3. Turn ignition off.

4 Remove coolant surge tank cap.

CAUTION: DO NOT REMOVE CAP OR OPEN COOLING SYSTEM DRAINS FROM A HOT SYSTEM. ALLOW SYSTEM TO COOL FIRST.

5. Drain at least 1.9 L (2 Qt.) of engine coolant from the cooling system by opening radiator drain valve or removing engine drain plug. Collect engine coolant in a container.

6. Disconnect engine coolant temperature sensor electrical connector.

7. Remove engine coolant temperature sensor from cylinder head.

8. Obtain replacement engine coolant temperature sensor (P/N 21025106).

9. Use appropriate tap to clean sensor mounting hole of any thread sealant residue.

10. Install engine coolant temperature sensor in cylinder head.

Torque:

Engine Coolant Temperature

Sensor: 8 Nm (71 in-lbs)

11. Inspect harness connector terminals for corrosion and/or evidence of engine coolant. If harness connector terminals are corroded or there is evidence of engine coolant, the harness connector must be replaced with new connector (P/N 12117087-includes: connector, terminals, wires, and splice sleeves).

12. Connect engine coolant temperature sensor connector.

13. Transfer engine coolant drained in step 5 into coolant surge tank. If necessary fill coolant surge tank to the FULL COLD range with 50/50 solution of correct type of antifreeze and clean water.

14. Start engine and check for leaks.

15. Run engine until upper radiator hose is hot, then add additional coolant if needed to bring the level to the FULL COLD level (1991-early 1997) or within the Min./Max. cold range (late l997-2001).

16. Install coolant surge tank cap.

PARTS REQUIREMENTS

CLAIM INFORMATION:

To receive credit for this repair during the warranty coverage period submit claim through the Saturn Dealer System using the appropriate Electronic Labor Time Guide and Labor Operation Code J6368 (Sensor, PCM Engine Coolant Temperature-Replace), and/or N6268 (Wiring and/or Connector Repair-Engine Coolant Temperature Sensor).

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Old 02-11-2005, 10:04 PM   #6
TheSaturnKid
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1997 SC2
Default Re: Lessons in ECT sensors

Quote:
I was recently inspired to write this because for some reason people thing the ECT is always the problem around here.
Mainly because it causes so many of the common problems in s-series cars, as the first design was a POS resin sensor.

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Old 04-29-2005, 07:31 PM   #7
marcusa
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Default Re: Lessons in ECT sensors

Why do people with ECT Sensor problems report that their gauge is reading low? Isn't the sensor for the gauge a separate one? Is it that the engine in open loop never heats up, or is it only the case sometimes?

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Old 04-29-2005, 07:42 PM   #8
David 93 SL2m
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Happy Re: Lessons in ECT sensors

Quote:
Originally Posted by marcusa
Why do people with ECT Sensor problems report that their gauge is reading low? Isn't the sensor for the gauge a separate one?
It depends on the model year:
  • The 1991 through 1995 S-Series engines use two coolant temperature sensors, one for the PCM and one for the dashboard gauge.
  • The 1996 through 2002 S-Series engines use one coolant temperature sensor, for the PCM. The PCM re-sends the information to the dashboard gauge.

...
As of Oct 2017
∙ 2002 SL1 128K
∙ 2004 VUE 120K
∙ 2007 ION3 108K
...
Past
∙ 1993 SL2 212K
∙ 1993 SC2 140K
∙ 1996 SC2 157K
∙ 1996 SC2 126K
∙ 2001 SC2, 145K
∙ 2002 L200 20K
...

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Old 04-29-2005, 07:52 PM   #9
David 93 SL2m
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Wrench Re: Lessons in ECT sensors

Quote:
Originally Posted by TheSaturnKid
Mainly because it causes so many of the common problems in s-series cars, as the first design was a POS resin sensor.
Don't forget the same "POS resin" sensor was used for the air intake also! If people still have the original non-brass version of the CTS in their air intake systems then I strongly suggest replacing it with the newer brass version.

I admit that I kept my original non-brass version of this sensor in my air intake system for over 12 years and over 156,000 miles. I changed both coolant temperature sensors plus the coolant temperature sensor that is used in the air intake system 1 month ago and saw my fuel economy increase substantially. For the record I had changed the EGR valve and the water pump about another month earlier so the fuel economy increase could have been due to the combination of these new parts.

...
As of Oct 2017
∙ 2002 SL1 128K
∙ 2004 VUE 120K
∙ 2007 ION3 108K
...
Past
∙ 1993 SL2 212K
∙ 1993 SC2 140K
∙ 1996 SC2 157K
∙ 1996 SC2 126K
∙ 2001 SC2, 145K
∙ 2002 L200 20K
...

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Old 04-29-2005, 10:27 PM   #10
Razorbak
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1996 SL2
Default Re: Lessons in ECT sensors

Quote:
Originally Posted by David 93 SL2m
Don't forget the same "POS resin" sensor was used for the air intake also! If people still have the original non-brass version of the CTS in their air intake systems then I strongly suggest replacing it with the newer brass version.
I don't think the resin tips are prone to cracking in air intake service, only in hot coolant service.

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Old 04-30-2005, 01:20 PM   #11
David 93 SL2m
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Happy Re: Lessons in ECT sensors

True, my old air temperature sensor (same part number as the coolant temperature sensor) did not have any cracks. But it was colored black. The temperature gauge on my dashboard was giving me questionable readings and installing a good thermostat did not make much of a difference with respect to this issue, so I figured my problem was one or the other of the two coolant temperature sensors. Since they are $14 +/- $5 each I chose to replace them both. And adding another sensor for the air intake didn't change the shipping fee so I bought it at the same time too.

Here are my old sensors. The picture is actually a hyperlink to a very large version of the same picture.

On the far left is the newer brass coolant temperature sensor used by the dashboard in the 1991 - 1995 models. The connection for the wiring harness differs from the coolant temperature sensor used by the PCM. It is also a tiny bit shorter in length and a little larger in diameter.

On the far right is the air temperature sensor that I used for a very long time. No cracking but it is black.

In the middle are 4 coolant temperature sensors. The left one is the newer brass type and the other three are the older non-brass types. Notice the non-brass sensor on the right actually has cracking visible.


...
As of Oct 2017
∙ 2002 SL1 128K
∙ 2004 VUE 120K
∙ 2007 ION3 108K
...
Past
∙ 1993 SL2 212K
∙ 1993 SC2 140K
∙ 1996 SC2 157K
∙ 1996 SC2 126K
∙ 2001 SC2, 145K
∙ 2002 L200 20K
...

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Old 05-01-2005, 10:08 AM   #12
Razorbak
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1996 SL2
Default Re: Lessons in ECT sensors

Quote:
Originally Posted by David 93 SL2m
Here are my old sensors. The picture is actually a hyperlink to a very large version of the same picture.
Great pictures. Here are a couple of my old sensor (resin-tipped)...



and the new one (brass-tipped)...


Last edited by Razorbak; 05-01-2005 at 10:17 AM..

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Old 05-22-2005, 09:21 PM   #13
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Default Re: Lessons in ECT sensors

thanks for the info guys.

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