Code 4.15 Coolant sensor low temp

[BryanB]

Code 4.15 Coolant sensor low temp...FIXED

Hey all,
I just picked up a 91 convertible from a friend. The check engine light came on after a short drive, Code 4.15 Coolant sensor low temp. I found it to be about 1 gallon low on coolant. I filled it, disconnected power for about 1 minute to reset the computer but am still getting the same code. Any thoughts?
I believe there is a sensor in the pass. head and one by the t-stat. The checked the wire at the head and it is connected. trying to clear this up. It runs a little rough with this code.

Thanks

Bryan

 

[BryanB]

I was just reading through the knowledge base and found this bulletin on the 86-88 models:
http://www.corvetteactioncenter.com...e-bulletin-low-coolant-warning-light-161.html

Says to disconnect the wire to the sensor and ground to the frame to see if it resets.
I will try this on the 91 to see if it may help

 

[ecss]

DTC 15 indicates a problem with the Engine Coolant Temperature Sensor which is screwed into the front edge of the intake manifold.

This is used by the computer to determine the fuel mixture and when the radiator fan comes on.

The connector has two wires. Yellow wire is 5 volts and Black wire is Ground.
If you unplug the connector and turn the ignition On you should measure around 5 volts from the Yellow wire to the Black wire.

If that tests good, the wiring is good and the problem is most likely the sensor.
Since you're loosing coolant, the sensor could be leaking.

With an ohm meter you can measure the resistance of the sensor at the following temperatures.

70 degrees F = 3.4K ohms
100 degrees F = 1.8K ohms
160 degress F = 450 ohms
210 degess F = 185 ohms

If you had a scan tool or data logging software you could monitor the output of the temperature sensor.

The temperature gauge sender is screwed into the passenger side head between spark plugs 6 and 8. It's used for the dash cluster temperature gauge.

 

[BryanB]

Thank you. I'll see if I can give it a quick look after work and before school tonight. h the ohm meter. My buddy has a scan tool but he's not available until this weekend

 

[BryanB]

And if you don't mind, where did you find this info? I'd like to learn about this and know where to reference it when needed...unless I put you on speed dial :L

 

[ecss]

And if you don't mind, where did you find this info? I'd like to learn about this and know where to reference it when needed...unless I put you on speed dial :L

The service manual written by GM for their techs. was published by Helms INC.
Some are 2 volumes and some are 1. I believe 91 was 1 volume and you could
purchase a LT5 engine supplement.

Here's a CD version. They claim it's the same as the hard copy and they are supposedly legit.
1991 Chevrolet Corvette Shop Service Repair Manual CD Engine Dirvetrain Wiring | eBay

Here's a legit hard copy. Usually you can find them for $50.00. The White cover version was the Preliminary version and the Red cover the final version.


1991 Corvette Shop Service Repair Manual Book Engine Drivetrain Electrical Guide | eBay

 

[BryanB]

Well no need to do any tests. Had the tester ready. Located the sensor by the thermostat only to find it had came unplugged. Everything works great now.
This makes the $5k I just paid for the car even better.

Thanks again

 

[ecss]

The connector should have a locking tab.

A new pigtail at NAPA is around $17.00.
Or a new connector is $8.00.

Coolant Temperature Temp Sensor ect Connector Plug Pigtail GM TPI TBI LT1 LS1 | eBay

You also need to find out where the 1 gallon of radiator coolant went. :L

A very common problem on the L98 is a head gasket leak in cylinder 7.
Look at all the spark plug electrodes for any sign of a steam cleaned look to it.

 

[BryanB]

Copy that. I had planned to do a full tune up once I got that code cleared. I have wondered about the low coolant. Nothing has got in the oil so thats a plus. Also not seeing any steam coming out of the exhaust. My friend has had the car for 2 years and only drove it once. He's also not very mechanically inclined.

 

[BryanB]

The connector should have a locking tab.

A new pigtail at NAPA is around $17.00.
Or a new connector is $8.00

Not sure why it was unplugged. The connector is intact. It is now locked into place

You also need to find out where the 1 gallon of radiator coolant went. :L

A very common problem on the L98 is a head gasket leak in cylinder 7.
Look at all the spark plug electrodes for any sign of a steam cleaned look to it.

I filled the system to include the overflow. Squeezed top and bottom rad hoses several times to get air out of the system. I then let it get up to temp until the thermostat open and fans kicked on. Let it cool. Did this process twice and checked fluid level. Seems to be fine. I have since drove it 2 trips of 25 miles each with no issues and no change in coolant level

I also checked several spark plugs, especially #5 & 7. They all look great.

Is it possible there was that big of an air pocket in the system that it was 1 gallon low? It does hold about 14.6 quarts

 

[ecss]

Should be around 16.1 quarts.

You were 1/4 low. ad
Can't see how it got that low with out a leak.

You can rent a radiator pressure tester from Auto Zone.
You could also replace the cap. which could have a bad seal.
The fill tanks are also know to leak at the bottom. Also verify the
low coolant sensor on the bottom of the fill tank is not leaking.

 

[BryanB]

Yeah, I will keep checking the level and look for leaks while hoping someone didn't do a good job filling it.

As for the capacity, I got the 14.6 quarts from this website:
1991 Corvette Specifications - C4 Corvette - www.corvsport.com

 

[ecss]

90 was the first year for the slant mounted radiator so 90 and 91 L98 engine coolant
capacity should be the same.

This is from the 90 Owners manual.
Internet information is free so beware of any advice or information you receive.
It's up to you to decide what's accurate.
:stirpot

 

[BryanB]

haha..thanks