I have been having problems with my CTS for a while now and I have finally decided that it must be something to do with the wiring. I have gone through three in the last 6 months. I have determined that there is a short or some other disturbance in the yellow wire coming off the sensor. I determined this by clearing the codes, connecting the black and yellow wires with a jumper, started car, got another code 15. I am told that this means it is a wiring problem. I then cleared the codes again and ran a jumper from the yellow wire to a good ground. Cleared the codes again, started it up and got another 15. My procedure tells me that this means that there is a problem with the yellow wire. Soooooo......I took my multi meter and did some tests. This is where you come in because when it comes to wiring and electronics, I am an idiot. I first tested for continuity on the yellow wire to the harness. It had continuity. The resistance on this wire was .1-.2 ohms with the ignition off. I couldnt get a value when the car was running, the meter would switch between k ohms and m ohms and stay at 0. The ground wire showed a resistance of 45 when the ignition was in the on position and 91 when the car was running. I then decided to get some values from the ECM pin #10, the CTS pin. On the yellow plug on the ECM pin 10 was as follows:

Top pin: 1.5 k ohms
Bottom pin: 1.7 k ohms

The black plug:
Top: 0
Bottom: 1.2 k ohms

I am not sure which one is the right plug as I am running an integrator for the SD conversion and the wires change colors. I am not sure if I am going about this right or if I have just made an *** of myself but I don't know where to go from here. Thanks.
bsa

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"If they do not run, Then they will die." - Stonewall Jackson

'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Comp Cam, Comp 1.6 Rockers, Lucas 23# injectors, Edelbrock headers, Flowmaster 3'' exhaust, gutted cat, Mallory coil, Mallory HyFire IV ignition box, Mallory Sidewinder 8mm wires, Autolite platinum plugs, K&N filters, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter

 

IROC,

Your method for checking the sensor wiring may not be completely valid. The ECM expects to see a resistance of between 5 and 100K ohms in temperature sensing circuits. A jumper wire is essentially ZERO ohms, and an open circuit is well over 100K ohms. If the ECM does not sense a resistance within that range, a DTC will be set.

The correct way is to measure the resistance of the sensor at a given temperature. You also need to check the continuity of the wiring between the sensor and the ECM. Measuring resistance of the ECM inputs is somewhat meaningless, since the inputs are very high impedance.

Since you've already determined that the black wire (NOT a ground wire, by the way) has between 45 and 91 ohms, you have a poor connection in that circuit. Both the yellow and black wires should have ZERO ohms from the sensor connector to the ECM harness.

If you want to verify the wiring, reconnect everything except the sensor. The black wire should have exactly 5.0 VDC to engine/chassis ground. If not, you have a connection problem along the black lead. Insert a 100 ohm resistor in the connector in place of the sensor, and check the voltage at the black wire again. There should still be exactly 5.0 VDC. If not, there is a poor connection in the black lead.

If you determine that the black wire has a low voltage/poor connection, check the black wire at the MAT sensor socket, and the black wire at the TPS sensor - they are all sourced from the same 5V regulated supply in the ECM. If the TPS and MAT have 5.0 VDC on the black wires but the CTS does not, there is definitely a connection problem along the wire. Start opening the plastic conduit along the right side of the engine and trace the black wire to its connections. There is a connector at the firewall near the distributor that is a junction point, and may be others along the harness.

Good luck.

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Later,
Vader
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"I know how to solve your problem, but I can't tell
you since you might use the information illegally..."
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Thanks Vader, Informative as always. I'll let you know.