Transmission Control Systems: Service Precautions

ELECTRONIC PRECAUTIONS

The 4L30-E Automatic Transmission has a Transmission Control Module (TCM) that is similar in some ways to the Engine Control Module (ECM). These modules are designed to withstand normal current draws associated with vehicle operation. However, care must be taken to avoid overloading any of the TCM circuits.

- In testing for opens or shorts, do not ground or apply voltage to any of the circuits unless instructed to do so by the appropriate diagnostic procedure.

- These circuits should only be tested with a high impedance multimeter (J-35029-A or equivalent), Tech-1 scan tool or special tools specifically intended for this type of testing.

- Power should never be removed or applied to any control module with the ignition in the ON position. Before removing or connecting battery cables, fuses, or connectors, always turn the ignition to the OFF position.

- If welding work is to be performed on the vehicle using an electrical arc welder, TCM and ECM should be disconnected before the welding operation begins.

- TCM and ECM connectors should never be connected or disconnected with the ignition on.

- Always backprobe a connector with DVOM test leads. Do not front probe unless special adapters are available that prevent terminal damage.

- Make all electrical tests with meter leads connected to the metal terminal ends. Never puncture the wire's insulation to obtain the reading.

- Whenever jumper wires are necessary to make electrical tests, always an appropriate jumper wire to insure electrical terminals are not damaged (such as KENT-MOORE J-35616 or equivalent).