For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

This circuit provides several data parameters (e.g. ECT, TP) to the TCM. The ECM pulls this circuit up to B+. The ECM induces a signal by toggling the B+ circuit to ground at a constant frequency of approximately 100 Hz. The TCM varies the duty cycle of this signal in order to transmit the data. The TCM interprets the variations in the duty cycle and separates out several encoded data parameters. The data transmission is one way, in a sequential order, a specific PWM signal represents each parameter value.

### Conditions For Running The DTC

Tests continuously

### Conditions for Setting the DTC

The TCM detects an open, short to ground, or short to B+ on the circuit.

### Action Taken When the DTC Sets

• | The TCM illuminates the Service Transmission Lamp (STL) and sends a MIL Request to the ECM on the second consecutive drive trip that the diagnostic runs and fails. The ECM then illuminates the MIL.

• | The ECM records the operating conditions in the Freeze Frame at the time of the MIL Request from the TCM.

• | The transmission operates in the Default Mode.

### Conditions for Clearing the MIL/DTC

• | The TCM turns off the STL as soon as the fault is no longer present.

• | The ECM turns off the MIL after three consecutive drive trips during which the TCM sends no MIL Request.

• | A History DTC clears after forty consecutive warm-up cycles, if no failures are present by this diagnostic or any other emission related diagnostic.

• | The scan tool clears the MIL/DTC.

### Diagnostic Aids

Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the TCM harness connector or a component harness connector. Using this kit will prevent damage to the harness connector terminals.

Check for the following conditions:

• | Poor connections at the TCM or at the component. Inspect the harness connectors for any backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure.

• | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the scan tool while moving any related connectors and any wiring harnesses. A change in the display may help to locate the fault.

### Test Description

The number(s) below refer to the step number(s) on the Diagnostic Table.

1. The voltage may vary since this is a variable pulse width signal.

#### DTC P1890 - ECM Data Input Circuit

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn off the ignition.
2. Disconnect the TCM.
3. Turn on the ignition with the engine off.
4. Use the DVM J 39200 in order to measure the frequency (Hz) on the ECM Data Input Circuit at the TCM harness connector.

Does the DVM indicate approximately the specified frequency?

100 Hz

Go to Step 11

Go to Step 3

3 |

1. Turn off the ignition.
2. Disconnect the ECM.
3. Use the DVM J 39200 in order to check the harness for continuity on the ECM Data Input Circuit from the ECM to the TCM.

Is the continuity indicated?

--

Go to Step 4

Go to Step 6

4 | Use the DVM J 39200 in order to check the continuity between the ECM Data Input Circuit and ground. Is the continuity indicated? | -- | Go to Step 7 | Go to Step 5
5 | Probe the ECM Data Input Circuit at the TCM harness connector with test light J 34142-B connected to ground. Does the test light illuminate? | -- | Go to Step 8 | Go to Step 9
6 | Repair the open or the high resistance in the circuit. Is the action complete? | -- | Go to Step 14 | --
7 | Repair the circuit that is shorted to ground. Is the action complete? | -- | Go to Step 14 | --
8 | Repair the circuit that is shorted to B+ Is the action complete? | -- | Go to Step 14 | --
9 | Check the ECM harness connector for a poor connection or poor terminal tension. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. Was a problem found and corrected? | -- | Go to Step 14 | Go to Step 10
10 | Important: This vehicle has a Theft Deterrent System which interfaces with the Engine Control Module (ECM). Program the new ECM with the frequency code of the theft deterrent module currently on the vehicle. Replace the ECM. Refer to Engine Controls, On Vehicle Service, ECM .

Is the action complete?

--

Go to Step 14

--

11 | Check the TCM harness connector for a poor connection or poor terminal tension. Refer to Engine Electrical, Troubleshooting Procedures, Checking Terminal Contact for proper procedure. Was a problem found and corrected? | -- | Go to Step 14 | Go to Step 12
12 |

1. Clear the scan tool.
2. Turn off the ignition for 15 seconds.
3. Start the engine.
4. Operate the vehicle within the conditions required for this diagnostic to run. Refer to Conditions for Running the DTC.
5. Check for any DTCs

Is DTC P1890 set?

--

Go to Step 13

Go to Diagnostic Aids

13 | Replace the TCM. Is the action complete? | -- | Go to Step 14 | --
14 |

1. Clear the DTCs with the scan tool.
2. Turn off the ignition for 15 seconds.
3. Start the engine.
4. Operate the vehicle within the conditions required for this diagnostic to run. Refer to Conditions for Running the DTC.
5. Check for any DTCs.

Is DTC P1890 set?

--

Go to Step 2

Go to Step 15

15 | Were there any additional DTCs noted during the Powertrain or Transmission OBD System Check that have not been diagnosed? | -- | Go to the applicable DTC table | Go to Step 16
16 | Does the Transmission now function properly? | -- | System OK | Go to Functional Test