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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1999 🢒 Eldorado 🢒 DTC 🢒 DTC P1640 Driver-1-Input High Voltage

Object Number: 244418 Size: MF
Engine Controls Components
Cell 20: PCM Power and Grounds
OBD II Symbol Description Notice
ESD Notice

Circuit Description

The PCM contains chips called Output Driver Modules that provide 7 switchable ground outputs for operating solenoids, relays, telltales, and other devices. Each of these ground outputs has an internal fault line that feeds back to the PCM's microprocessor. ODM #1 can also sense high voltage coming in which might damage the chip. DTC P1640 is used to monitor ODM #1's overvoltage sense line.

Conditions for Running the DTC

Engine running at least 10 seconds.

Conditions for Setting the DTC

Overvoltage is sensed for 2 seconds.

Action Taken When the DTC Sets
    •  The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
    •  The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC
    •  The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
    •  A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
    •  A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.
    • 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.

Diagnostic Aids

Since an overvoltage at ODM #1 should also trigger DTC P0563 the diagnosis for DTC P0563 may be used if vehicle voltage is actually too high.

A loose or faulty connection at generator L terminal may cause DTC P1640 to set intermittently.

Test Description

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

  1. If ignition voltage and IPC battery voltage are within 1.5 volt of each other, there may be a system voltage problem. If they are not within 1.5 volt of each other, find out why the PCM is different.

    2.

  2. Checking if PCM ignition voltage is actually displaying system voltage.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Start and idle the engine.
  2. Using a scan tool view the Ignition 1 display.
  3. Compare this voltage to the voltage displayed by the vehicle message center.

Are PCM and vehicle voltage readings different by more than the value specified?

1.5 volts

Go to Step 3

Fault not present. Refer to Diagnostic Aids

3

Using DMM J 39200 measure voltage to ground on Engine Compartment Fuse/Relay Center fuse C7 (installed).

Is voltage measured and the Ignition 1 voltages different by more than the value specified?

1.5 volts

Go to Step 4

Perform Charging System Check

4
  1. Check for high resistance in CKT 639.
  2. Repair high resistance if needed.

Was a repair made to CKT 639?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 5

5
  1. Check PCM terminal contact at connector C1 terminal 19 and connector C2 terminal 37.
  2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 6

6

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the replacement complete?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

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