DTC P1621 Control Module Long Term Memory Performance. Cadillac Concours 1996

For 1990-2009 cars
Engine Controls Components
PCM Power and Grounds
OBD II Symbol Description Notice
ESD Notice

### Circuit Description

The PCM contains a data storage unit which can save critical data even when battery power is removed. This unit, the Electrically Erasable Programmable Read Only Memory (EEPROM), is used by the PCM to store TP Sensor/Idle Learned values, Transaxle Adapt values and Transaxle Oil Life Index. The EEPROM has several locations available to store this information. If the PCM detects a problem in one location of the EEPROM, it will store the data in another location. If the PCM runs out of good locations in the EEPROM to store data, it will set DTC P1621. The PCM stores the same data in its Keep Alive Memory so that even if the EEPROM is bad and DTC P1621 sets, the operator will not notice any difference in vehicle operation. Even after a DTC P1621 is set, the PCM will continue to look for good locations in the EEPROM in which to store data and if it finds good locations, DTC P1621 will become a history DTC. The EEPROM is soldered into the PCM and cannot be serviced separately. If a current DTC P1621 is set, the PCM must be replaced.

### Conditions for Setting the DTC

#### Test Condition

Tested always.

#### Failure Condition

A failure to store data in all EEPROM locations has occurred.

### Action Taken When the DTC Sets

• | The Malfunction Indicator Lamp (MIL) will not illuminate.

• | No message will be displayed.

### Conditions for Clearing the DTC

• | A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.

• | A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

• | Use a scan tool to clear DTCs.

• | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.

### Test Description

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

1. If DTC P1621 is set current, the PCM cannot find another location to store the data, so the PCM must be replaced.

2. Cycle the ignition to give the PCM a chance to find a place to store the data. If the DTC resets, no place can be found so the PCM must be replaced.

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

2

1. Turn the key ON.
2. Using a scan tool select DTC Info. select Fail This Ign.

Has this DTC failed this ignition?

--

Go to Step 4

Go to Step 3

3

1. Clear DTC P1621.
2. Cycle ignition ON and OFF several times slowly, ignition ON for 10 seconds then ignition OFF for 30 seconds.
3. Using a scan tool check DTC Info select Test Fail SCC.

Has this DTC failed since DTCs were cleared?

--

Go to Step 4

Fault not present

4 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --