DTC P1660 Cooling Fan Control Circuits. Cadillac Concours 1996

For 1990-2009 cars

Refer to

#### Cooling Fans/ Relays

Engine Controls Components
EBTCM/ Generator/ A/C Relay/ RSS
OBD II Symbol Description Notice
ESD Notice
for wiring view.

### Circuit Description

The PCM contains a chip called a Quad Driver Module that provides 4 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 PCMs microprocessor. When the output is OFF, the quad driver should receive the 12 volts fed to the solenoid, relay, etc. When the output is ON, the quad driver should receive 0 volt since it is grounding the output. If it receives 0 volt when the output is OFF or 12 volts when the output is ON, it sets the fault line low. DTC P1660 is used to monitor the fault line of the cooling fan control relay output.

### Conditions for Setting the DTC

#### Test Conditions

• | Ignition voltage between 10 and 16 volts.

• | PCM in Closed Loop fuel control.

• | Engine running for at least 10 seconds.

#### Failure Condition

Fault line is low 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

Review the Freeze Frame and Failure Records that were stored when this DTC set. Check these conditions to determine the odometer reading and driving conditions under which this DTC set.

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. Turn all HVAC controls to OFF.
3. Using a scan tool select the output tests for Fan Relays.
4. While viewing the Quad Driver 1 display, command All Relays OFF.

Does the display indicate OK?

--

Go to Step 3

Go to Step 8

3 | While viewing the Quad Driver 1 display, command All Relays ON. Does the display indicate OK? | -- | Go to Step 4 | Go to Step 5
4 | Is there a cooling fan operation complaint or fault suspected? | -- | Go to Electric Cooling Fan Diagnosis (Functional Check) | Fault not present. Refer to Diagnostic Aids
5 | While viewing the Quad Driver 1 display, command Fan Relay 1 ON. Does the display indicate OK? | -- | Go to Step 7 | Go to Step 6

6

1. Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
2. Disconnect PCM connector C2.
3. Remove fan relay 1 (low speed).
4. Turn the key ON.
5. Using DMM J 39200 measure the voltage to ground at PCM connector C2 terminal 32.

Is the voltage the same or less than the value specified?

0.5 volts

Go to Step 18

Go to Step 16

7

1. Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
2. Disconnect PCM connector C2.
3. Remove fan relays 2 and 3.
4. Turn the key ON.
5. Using DMM J 39200 measure the voltage to ground at PCM connector C2 terminal 33.

Is the voltage the same or less than the value specified?

0.5 volts

Go to Step 18

Go to Step 17

8 | With All Relays still commanded OFF observe the operation of both cooling fans. Is either fan operating? | -- | Go to Step 9 | Go to Step 10

9

1. Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
2. Disconnect PCM connector C2.
3. Turn the key ON.
4. Using DMM J 39200 measure the voltage to ground at PCM terminal 32.

Is the voltage the same or more than the value specified?

10.0 volts

Go to Step 14

Go to Step 15

10

1. Record the fluid life indexes, turn the key to LOCK and wait 30 seconds.
2. Disconnect PCM connector C2.
3. Turn the key ON.
4. Using DMM J 39200 measure the voltage to ground at PCM terminals 32 and 33.

Is the voltage the on both terminals the same or more than the value specified?

10.0 volts

Go to Step 18

Go to Step 11

11 | Was the voltage measured in Step 10 low for both terminals? | -- | Go to Step 13 | Go to Step 12
12 | Repair the open circuit or replace the open fan relay for the CKT that measured low in Step 9. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

13

1. Repair the cause of no voltage to both circuits.
2. Replace the fuse if blown.
3. Possible causes are:

• | Open in both CKT 335 and CKT 473.

• | Open in CKT 2340 to both sets of relays.

• | Short to ground in CKT 2340 to relays (blown fuse).

• | Shorted fan relay(s) (blown fuse).

• | Short to ground in CKT 2340 to A/C compressor relay (blown fuse).

• | Shorted A/C compressor relay (blown fuse).

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

--

14 | Repair short to ground in CKT 473. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
15 | Repair short to ground in CKT 335. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
16 | Repair short to voltage in CKT 335. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --
17 | Repair short to voltage in CKT 473. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | --

18

1. Check terminal contact at the PCM.
2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 19

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