Do I need a new ecu

[lokitruck]

Truck threw code 15. It’s been doing this for a while now. (CTS is reading abnormally low readings). I have replaced it already and still same thing. Truck is constantly stalling out when I’m braking. Is my ecu bad? I should say I’ve done plugs, wires, fuel pump, fuel filter , egr valve, TPS, and new distributor

 

[PlayingWithTBI]

Which CTS did you replace, the one by the T-Stat housing (feeds ECM) or the one between cylinder #s 1 & 3 (feeds gauge)? Not very often (but not unheard of) the ECM goes out.

Here's a troubleshooting guide that may help.
TBIcodes.pdf

 

[evilunclegrimace]

Truck threw code 15. It’s been doing this for a while now. (CTS is reading abnormally low readings). I have replaced it already and still same thing. Truck is constantly stalling out when I’m braking. Is my ecu bad? I should say I’ve done plugs, wires, fuel pump, fuel filter , egr valve, TPS, and new distributor

What year, engine, transmission?

 

[lokitruck]

I replaced the sensor by the thermostat. 92 350 tbi 700r4

 

[Schurkey]

What is the scan tool showing for coolant temperature?

 

[lokitruck]

I don’t have a scan tool. I’m just going off of the service engine soon code and the stalling out every time I stop

 

[Schurkey]

Diagnosing a failed ECM or a driveability complaint without a scan tool is going to be very labor intensive.

Do yourself a favor, look at the data stream with a REAL scan tool.

Failing that, inspecting the resistance of the coolant sensor by disconnecting the wire harness AT THE COMPUTER and testing the appropriate wires in the harness connector would tell you whether the sensor AND WIRE HARNESS are in usable condition. Be sure to use a 10 Megohm input impedance ohmmeter. Most are these days. Older ones may not be. More than 10 megohm is OK, less is not.

A failed sensor and a failed sensor wire harness look the same to the computer.

 

[east302]

The factory manuals have been scanned to PDF format here:


https://www.gmt400.com/threads/88-95-service-manuals.43575/

From the 1992 manual, here is the diagnostic for Code 15.

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[lokitruck]

After checking the wires with the ohmmeter im only reading 5ohms at the cts

 

[Schurkey]

After checking the wires with the ohmmeter im only reading 5ohms at the cts

5 ohms represents a coolant temperature of...what...five hundred degrees?

Sure that isn't a decimal error? 500 ohms? 5000 ohms?

Get a scan tool.