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Old 11-26-2006, 06:11 PM   #1
bigfish00jk
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Geo Metro Code 15 Help.

I have a 1994 Geo Metro whose check engine light is on. I read the code by placing the spare fuse in and reading the flashes.I read that there was 1 flash a pause then 5 flashes. Code 15 which is the coolant sensor. I went to Autozone on Friday and bought a new one and replaced it today. I reset the check engine light. Today I was driving the Metro around town and the light came back on again. Once again it still says code 15. Whats going on?
Thanks for the help.
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Old 11-26-2006, 06:44 PM   #2
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Re: Geo Metro Code 15 Help.

where was the sensor you replaced? one giving you the code is the one thats screwed into the side of the throttle body. if you replaced the one by the thermostat by upper radiator hose thats the one for the guage
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Old 11-26-2006, 09:24 PM   #3
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Re: Geo Metro Code 15 Help.

Hmm..
I think I replaced the right one but I'm not sure. I'm not really good with part names and placement in a car. I'm not too car savvy (which is why I use my Hayne's manual) but I can tell you that I had to lift up the air filter so that I could get to the coolant sensor. I had to remove the electrical connector first then I unscrewed the sensor. When I removed the sensor some anti-freeze came out. Does that help any? Did I replace the wrong one? Thanks,
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Old 12-12-2006, 07:49 PM   #4
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Re: Geo Metro Code 15 Help.

I have 2 1994 Geo Metros with the same problem - the check engine light is on with a code 15 - coolant temperature sensor - overheat. They both run cool. I have replaced the sensor - no help. I have also tested the new and old sensors with ohm meter at verius temps on stove with a thermometer - all check good. Any ideas?
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Old 12-15-2006, 10:58 AM   #5
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Unhappy Re: Geo Metro Code 15 Help.

I have a 94 4-Dr Geo Metro (5 Speed Manual) with the same CEL Code 15 Problem (Car runs fine with NO Overheating, Temp gauge is right in the middle). I Can remove the NEG Bat cable to reset the CEL (Check Engine Light) and sometimes drive the car for 100+ Miles before the CEL Comes back on with the same CODE-15 Error. I Also tried swaping out a new coolant temp sensor but that error code is actually CODE 14 (The correct Sensor is located on the side of the TB, PS Of the car and has a Gray/White stripe wire and a Light Green/Black wire running to it). Code-15 error is either 1 of 2 Things. The Gray/White wire, which runs from one side of the Temp Sensor to the ECM is shorted to ground somewhere (Do a continuity check to test this) OR, If this wire tests out good with no short, The ECM computer Is bad.... . I my case, I did the continuity test on the Gray/White wire by removing the ECM and disconnecting both wiring harness plugs (Remove both + and - Battery cables from the BAT 1st BEFORE Disconnecting the Plugs on the ECM), Then found the Gray White wire on the ECM plug, Then ran approx 3 ft of spare 18 ga wire from the Coolant temp sensor plug Gray/White wire terminal to inside the car with the door open. Connected my Fluke meter leads to the Gray/White wire on the ECM Plug and to the 3ft wire I ran from the Gray/White Coolant plug terminal and tested for a short to ground and continuity.....It passed the test! Nothing else left to test according to the error code info.......My ECM Is bad..... . If you have to replace the ECM, You need to find one with the correct Model # and year on it (89-91 wont work on 92-94's) You can find them on E-Bay but make sure you match the numbers. Some ECM's are for Auto trans, Some for manual, Some have Federal Emmisions (Other 49 states), Some say CALifornia emmsions.......I'm still dealing with the problem because I haven't found a match for mine on E-Bay yet......I'm hitting the local Junkyards this weekend too! I Have 2 spare good ECM's at the house now, 1 from a 94 Auto trans Metro and 1 from a 92 Manual Trans Metro....The Manual trans is not a match for my car.....Bummer! Here's an example of the info you need to match on your ECM if it's bad.


Last edited by GM Line Rat; 12-16-2006 at 10:24 AM.
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Old 12-15-2006, 01:29 PM   #6
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Re: Geo Metro Code 15 Help.

CODE 15

Trouble Code 15 indicates that the Coolant Temperature Sensor (CTS) is reporting abnormally low readings. CTS is used to control fuel mixture, timing, idle speed, TCC and EGR operation, among others. The thermistor used has a high-resistance when cold, lowering as the coolant warms.

Code 15 will set if:

- temperature reported is < -37.30 deg F (-38.5 deg C)

Typical thermistor resistances expected are:


Deg C Deg F Resistance (ohms)
100 212 177
70 158 332
40 104 1459
20 68 3520
5 41 7280
-5 23 12300
-20 -4 28680
-40 -40 100700


Typical causes may include:

1) Open circuit in CTS-ECM harness

2) Defective Coolant Temperature Sensor

3) Open sensor ground circuit

4) Defective ECM
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Old 12-16-2006, 10:34 AM   #7
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Re: Geo Metro Code 15 Help.

Diagnostic Flow charts for Code 15 and Code 14 and ECT Wiring





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Old 01-08-2007, 06:48 PM   #8
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Re: Geo Metro Code 15 Help.

Well, I FINALLY figured out my code 15 Error and the source of the problem! After doing several checks with my VOM (Volt/Ohm meter) in different locations on the Gray/White stripe wire for the presence of 5 volts (From the ECM to the ECT Sensor plug.....No shorts, 5 volts always present (Key in on position, Engine off, ECT Plug disconnected)....Then I proceeded per instructions to check back the Light Green/Black stripe wire on the ECT Temp sensor plug for the stated voltage drops at different engine temps.....Bingo!!!.....Voltage drops were out of specified range!.....Problem was....... Poor grounding contact of the Black/Green stripe and Black/Blue stripe wires on the back of the intake manifold. My 94 4Dr Metro had 2 sets of ECM grounds that are grounded on the back of the intake manifold. 1 set of grounds is the Black/Green stripe and Black/Blue stripe .....The other set was 2, Black with yellow stripes on them. I removed both sets, cleaned them up real good with a wire brush, cleaned the mounting surface(s) on the back of the intake manifold also, tightened both ground bolts good (10mm).....It's been 3 days and over 150 miles of driving.......No CEL or code 15 coming on anymore.... .....Luckly, I have a good friend at the local boneyard who allowed me to pull a matching ECM from a donor car and check for a bad ECM.....Wasn't the problem after all!
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Old 06-08-2016, 11:44 AM   #9
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Re: Geo Metro Code 15 Help.

Dude! Thank you guys so much for the help. I followed GM Line Rat's advice and got a code 14! So hopefully all I have to do is replace the ECT sensor and we'll see what happens!

Well, after replacing the ECT sensor, I still got a check engine light, Code 15. So it must be something in the wiring or the ECM. The grounds look good at least. Thanks for all the help anyway.

I might just leave it and drive it till the thing dies.
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