For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC B101D XX: ECU Hardware

### Circuit/System Description

The internal fault detection is handled inside the control module. The symptom byte listed in the DTC Descriptor is for engineering reference only. No external circuit diagnosis is involved.

### Conditions for Running the DTC

The module runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

### Conditions for Setting the DTC

The module has detected an internal malfunction.

### Action Taken When the DTC Sets

The module refuses all additional inputs.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

### Diagnostic Aids

• | This DTC may be stored as a history DTC without affecting the operation of the module.

• | If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.

• | If this DTC is retrieved as both a current and history DTC, replace the module that set the DTC.

### Circuit/System Verification

Verify that DTC B101D is not set.

⇒ | If the DTC is set, replace the module that set the DTC.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for module replacement, setup, and programming