For 1990-2009 cars

### Circuit Description

The Powertrain Control Module (PCM) is the control center of the fuel injection system. The PCM receives the information from the various sensors, and controls the systems that effect the vehicle performance. The PCM also performs the diagnostic function of the system. The PCM can recognize any operational problems, alert the driver through the malfunction indicator lamp (MIL) (Check Engine), and store a DTCs which identify the problem areas in order to aid you in making repairs. An electrically erasable programmable read only memory (EEPROM) houses the program information and the calibrations required for the engine, the transmission, and the powertrain diagnostics operation. The PCM uses a value called a checksum for an error detection of the software. The checksum is a value that is equal to all of the numbers in the software added together. The PCM adds all of the values in the software. If that value does not equal the checksum value, this indicates that there is an error in the checksum.

### Conditions for Setting the DTC

The PCM detects more than 3 incorrect checksums.

### Action Taken When the DTC Sets

• | The malfunction indicator lamp (MIL) will illuminate.

• | The PCM will attempt to record the operating conditions at the time during which you detect this failure, however, since this is a internal PCM failure, you cannot rely on this information. This information will store in the Freeze Frame and Failure Records buffers.

• | A history DTC stores.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | The MIL/DTCs can be cleared by using the scan tool.

### Test Description

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

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.

2. The replacement PCM must be reprogrammed and the crankshaft position system variation procedure must be preformed. Refer to the latest Techline procedures for PCM reprogramming and Powertrain Control Module (PCM)

#### DTC P0601-PCM Memory

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 | Replace the PCM. Is the action complete? | -- | Go to Step 3 | --
3 |

1. Using the scan tool, clear the DTCs.
2. Start the engine and idle at normal operating temperature.
3. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic has ran and passed?

--

Go to Step 4

Go to Step 2

4 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK