The transmission that is used in this vehicle is the Hydra-Matic 4L30-E. The transmission is a four speed automatic with a torque converter clutch that provides a direct coupling to the engine when desired. The gear changes, the line pressure, and the torque converter clutch operation are controlled by an electronic control system. This system uses a separate Transmission Control Module (TCM). Certain specific signals are sent between the TCM and the ECM on the dedicated circuits for each signal. The TCM system also has self diagnostic capabilities.

This section is designed as the starting point for all of the Automatic Transmission diagnosis. This section contains a basic description of the Catera transmission, detailed information on the TCM, the on-board diagnostics, and selected other components as well as references to other sections for detailed information on other related subsystems that are not covered here. Before diagnosing this vehicle, you should read and be familiar with the following:

Base engine, transmission, and non-emissions subsystem Information can be found in the following areas:

Important: Do not clear the DTCs unless you are instructed to do so by a diagnostic procedure.

If the Engine MIL illuminates, start with the Powertrain OBD System Check in Engine Controls. If only the Service Transmission Lamp (STL) illuminates, start with the Transmission On-Board Diagnostic (OBD) System Check in this section.

While performing a diagnostic procedure, you may need to gain access to certain components. Read the On-Vehicle Service procedures for those components.

During diagnosis or if a wiring problem is found, refer to Engine Electrical. Engine Electrical contains complete information on vehicle wiring and also includes the following information:

After diagnosing a problem, in addition to repairing the discovered problem, perform the verification procedure which is the last few steps at the end of almost all of the diagnostic tables. Here, you may be instructed to clear the DTCs. In order to clear the DTCs, refer to Clearing DTCs later in this section. In order to verify a repair, you must duplicate the conditions when the customer's complaint occurs or if a DTC sets. You must duplicate the test conditions for that DTC (listed on the facing page of the trouble chart) and see if the DTC sets. Test the repair under the proper conditions for the diagnostic to run, and if the DTC does not re-set, chances are good that the repair is successful.

The diagnostic procedures used in this section are designed to find and repair problems that relate to the transmission controls system. The general approach is to find the appropriate diagnosis for a problem by using the basic steps described below.

1. Understand the customer's complaint. It is critical that the technician understands what the customer's complaint is. Failure to understand the customer's complaint may lead to misdiagnosis or an unnecessary diagnosis. Among other things, the technician must know whether the condition is present at all times, only under certain circumstances, or truly intermittent (random). This will assist the technician in duplicating and diagnosing the problem. Another reason that the technician must understand the customer's complaint is so that the technician may determine whether the complaint requires service or if the vehicle operation is normal. Trying to diagnose a complaint that is normal will waste time and may result in unnecessary service.
2. Are the Diagnostics working properly? If the Engine MIL illuminates, start with the Powertrain OBD System Check in Engine Controls. If only the Service Transmission Lamp (STL) is illuminated, start with the Transmission On-Board Diagnostic (OBD) System Check in this section.
3. Are the DTCs displayed? If a DTC is identified by the diagnostics, the OBD System Check will direct you to the appropriate chart.

Notice:  Lack of basic knowledge of this transmission when performing the diagnostic procedures could result in incorrect diagnostic results or damage to the transmission components. Do not, under any circumstances, attempt to diagnose a transmission problem without this basic knowledge.

You must be familiar with some of the basics of transmission operation and electrical diagnosis in order to use this section of the service manual.

For any test that requires probing the TCM harness connector or a component harness connector, use the Connector Test Adapter Kit J 35616 . Using this kit will prevent damage to the harness connector terminals.

Whenever checking Hydra-Matic 4L30-E transmission fluid, refer to Transmission Fluid Check in this section.

The Transmission Control Module (TCM) is an electronic device which monitors various inputs in order to control various transmission functions. These functions include shift timing and quality, TCC apply and release, line pressure, and transmission diagnostics. The TCM receives input from electrical sensors, switches, solenoids and other components in order to process for use within the control program of the TCM. Based on this input information, the TCM controls certain transmission output functions and devices. The TCM is located behind the kick panel beneath the glove compartment, in the passenger compartment.

The DLC is a 16-pin connector that provides the technician a means of accessing serial data for aid in diagnosis. This connector allows the technician to use a scan tool in order to monitor the various system parameters and display the Diagnostic Trouble Code (DTC) information. The DLC is located within the driver's compartment, underneath the dash on the driver's side.

The Catera uses ISO serial data and communicates with the scan tool on DLC pin 7. Most other GM OBD II vehicles use Class 2 serial data on DLC pin 2. Both the ECM and the TCM communicate with the scan tool by using the ISO serial data circuit.

The Transmission Control Module (TCM) controls a dedicated Service Transmission Lamp (STL) which illuminates when certain non-emissions driveability conditions which relate to the TCM diagnostics report a fail. The Service Transmission Lamp (STL) is located in the Instrument Panel Cluster (IPC).

The TCM has no direct control of the engine MIL, but if a transmission fault occurs that is emissions related, the engine MIL must illuminate. A MIL Request circuit between the ECM and the TCM provides a means for illuminating the MIL, even though the fault was detected by the TCM. This circuit is pulled up to B+ within the ECM. In order to illuminate the MIL, the TCM pulls the circuit low. The ECM detects this and DTC P1700 is set (in the ECM), which illuminates the MIL.

Notice: Do not backprobe Weatherpack connectors. The connectors are sealed for operation in an exposed environment. Backprobing may damage the seal which could eventually cause the connector to fail due to corrosion.

A wiring harness electrically connects the TCM to various sensors, solenoids, and relays within the system. Many of the connectors are environmentally-protected (Weatherpack).

For any test that requires probing the TCM harness connector or a component harness connector, use the Connector Test Adapter Kit J 35616 . Using this kit will prevent damage to the harness connector terminals.

System diagnosis will often require that electrical readings at these connectors in order to observe system performance. Anytime a connector requires separation, take care so that the pins or the terminals are not damaged.

When disconnecting the transmission external connector, additional DTC(s) will be set. Clear these DTC(s) after reconnecting the external connector. Use of a test jumper harness will aid in diagnosis of the transmission wiring and system components. Refer to Transmission Electrical Connector in this section.

The TCM uses the following information sensors in order to gather the data for electronically controlling transmission functions:

Certain additional signals are sent between the ECM and the TCM on dedicated circuits for each signal.

The Hydra-Matic 4L30-E uses a line pressure control system which has the ability to adapt the system's line pressure in order to compensate for normal wear of clutch fiber plates, seals, springs, etc. This learning feature is similar in function to fuel control (integrator/block learn).

The Hydra-Matic 4L30-E transmission only uses the adapt function for the 1-2 upshift. The TCM monitors the engine speed in order to determine if the shift is occurring too fast (harsh) or too slow (soft) and adjusts the pressure control solenoid in order to maintain the correct shift feel. The line pressure can adapt to values ranging from 5 psi below, to 10 psi above the normal line pressure.

The TCM controls the transmission operation in three modes: Economy mode, Performance mode, and Winter mode. The driver determines the transmission operating mode through the Performance/Economy mode switch and Winter mode switch.

If a major electrical system failure occurs which could affect vehicle safety or damage the transmission during normal operation, the TCM enters a default mode. In the default mode, the transmission operates in the following manner:

Important: When the system failure is not due to the TCM, and the TCM is functioning properly, the transmission will operate in 2nd gear when the selector lever is in the Manual 1st position. In this situation, the TCM operates the shift solenoids in a 2nd gear state.

With both shift solenoids off (4th gear state), the transmission will operate in 4th gear when the gear selector lever is in the Drive range position. However, the driver has some flexibility in the gear selection during default operation by moving the gear selector lever. The following table lists the operating characteristics in default mode.