On Board Diagnostics II PCED

1999 PCED On Board Diagnostics II

SECTION 5: Pinpoint Tests

DS: Air Conditioning Pressure (ACP) Sensor

DS1 DTC P1461: CHECK ACP V PID

Connect scan tool.
Key on, engine off.
Access ACP V PID.

Is ACP V PID less than 4.9 volts?

Yes	No
The ACP circuit voltage is now below the maximum. GO to DS18 to determine if an intermittent condition exists.	KEY OFF. A hard fault is present. GO to DS2 .

DS2 CHECK VOLTAGE BETWEEN VREF AND SIG RTN CIRCUITS TO ACP SENSOR

Disconnect ACP sensor.
Key on, engine off.
Measure voltage between VREF and SIG RTN circuits at the ACP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
GO to DS3 .	VREF is out of range, or SIG RTN circuit to ACP sensor is open. KEY OFF. GO to Pinpoint Test Step C1 .

DS3 INDUCE OPPOSITE ACP SIGNAL

Key on, engine off.
Again access ACP V PID.

Is ACP V PID now less than 4.9 volts?

Yes	No
KEY OFF. REPLACE ACP sensor. (REFER to the Climate Control System General Information, Section 412-00 in the Workshop Manual). START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	KEY OFF. GO to DS4 .

DS4 CHECK ACP CIRCUIT FOR SHORT TO VREF IN HARNESS

Disconnect scan tool from DLC.
Disconnect PCM.
Measure resistance between ACP and VREF circuits at the ACP sensor harness connector.

Is resistance greater than 10,000 ohms?

Yes	No
GO to DS5 .	REPAIR short circuit. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS5 CHECK ACP CIRCUIT FOR SHORT TO POWER IN HARNESS

Key on, engine off.
Measure voltage between ACP circuit at the ACP sensor vehicle harness connector and chassis ground.

Is voltage less than 1.0 volt?

Yes	No
For Escort/Tracer: KEY OFF. GO to DS6 . All others: REPLACE PCM (refer to Section 2 , Flash EEPROM). START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	REPAIR short circuit. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS6 CHECK FOR OPEN ACP CIRCUIT IN HARNESS

Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.

Measure resistance of ACP circuit between PCM harness connector pin and the ACP sensor harness connector.

Is resistance less than 5.0 ohms?

Yes	No
GO to DS7 .	REPAIR open circuit. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS7 CHECK PCM

Reconnect PCM.
Connect a jumper wire between the ACP and SIG RTN Circuits at the ACP sensor harness connector.
Key on, engine off.
Access ACP V PID.

Note: If the scan tool is now unable to communicate, follow NO Action to Take.

Is ACP V PID now less than 4.9 volts?

Yes	No
REPLACE ACP sensor. (REFER to the Climate Control System General Information, Section 412-00 in the Workshop Manual.) START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	REPLACE PCM (refer to Section 2 , Flash EEPROM). START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS10 DTC P1462: CHECK ACP V PID

Connect scan tool.
Key on, engine off.
Access ACP V PID.

Is ACP V PID greater than 0.15 volt?

Yes	No
The ACP circuit voltage is now above the minimum. GO to DS18 to determine if an intermittent condition exists.	KEY OFF. A hard fault is present. GO to DS11 .

DS11 CHECK VOLTAGE BETWEEN VREF AND SIG RTN TO ACP SENSOR

Disconnect ACP sensor.
Key on, engine off.
Measure voltage between VREF and SIG RTN circuits at the ACP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
GO to DS12 .	VREF is out of range. KEY OFF. GO to Pinpoint Test Step C1 .

DS12 INDUCE OPPOSITE ACP SIGNAL

Connect a jumper wire between ACP and VREF circuits at the ACP sensor harness connector.
Key on, engine off.
Access ACP V PID.

Note: If any scan tool communication concern occurs, remove jumper immediately and go directly to DS13 .

Is ACP V PID greater than 4.0 volts?

Yes	No
REPLACE ACP sensor. (REFER to the Climate Control System General Information, Section 412-00 in the Workshop Manual.) START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	GO to DS13 .

DS13 CHECK ACP CIRCUIT FOR SHORT TO PWR GND OR SIG RTN IN HARNESS

Key off.
Disconnect scan tool from DLC.
Disconnect PCM.
Measure resistance between ACP and SIG RTN circuits at the ACP sensor harness connector.
Measure resistance between the ACP circuit at the ACP sensor harness connector and the battery negative post.

Are both resistances greater than 10,000 ohms?

Yes	No
GO to DS14 .	REPAIR short circuit. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS14 CHECK ACP CIRCUIT FOR OPEN IN HARNESS

Note: Refer to the PCM connector pin numbers in the beginning of this Pinpoint Test.

Measure resistance of ACP circuit between PCM harness connector pin and the ACP sensor harness connector.

Is resistance less than 5.0 ohms?

Yes	No
GO to DS15 .	REPAIR open ACP circuit. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS15 CHECK FOR THE A/C CLUTCH TO ENGAGE

Reconnect ACP sensor.
Key on, engine off.
While listening for the A/C clutch to engage, turn the A/C on. Repeat if necessary.
Key off.

Did the A/C clutch engage when the A/C was turned on?

Yes	No
REPLACE PCM (refer to Section 2 , Flash EEPROM). START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	GO to DS16 .

DS16 VERIFY A/C SYSTEM HAS A REFRIGERANT CHARGE

Restore vehicle.
Verify that the A/C system has a refrigerant charge. (Refer to the Electrical/Climate Control Systems Group in the Workshop Manual).

Does the A/C system have a refrigerant charge?

Yes	No
REPLACE PCM (refer to Section 2 , Flash EEPROM). START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	REPAIR A/C system, REFER to Climate Control System General Information, Section 412-00. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS18 CHECK FOR INTERMITTENT ACP CIRCUIT FAULT

Key on, engine off.
Access ACP V PID.
Observe ACP V PID for an indication of a fault while completing the following (a fault will be indicated by a sudden change in ACP V PID voltage):

Shake, wiggle, bend the ACP, SIG RTN and VREF circuits between the ACP sensor and the PCM.
Lightly tap on the ACP sensor (to simulate road shock).

Is a fault indicated?

Yes	No
ISOLATE fault and REPAIR as necessary. PERFORM PCM Reset to clear DTC(s). START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	Unable to duplicate or identify fault at this time. GO to Pinpoint Test Step Z1 .

DS20 DTC P1463: VERIFY A/C CLUTCH CAN DISENGAGE

A/C and defroster off.
Start engine.
Verify that the A/C clutch disengages.

Is the A/C clutch disengaged?

Yes	No
KEY OFF. GO to DS21 .	GO to Section 3 , Symptom Chart 24 (A/C Compressor Runs Continuously, A/C Always On) to diagnose the always engaged A/C clutch.

DS21 CHECK FOR VOLTAGE AND GROUND TO A/C CLUTCH (USING NON POWERED TEST LAMP)

Note: If voltage and ground to A/C clutch has already been checked in the Section 3 Symptom Charts, or the A/C clutch can be heard clicking on when the A/C is turned on, go to the question at the end of this test step.

Disconnect A/C cycling switch. Install a jumper wire in the A/C cycling switch vehicle harness connector (to complete the circuit).
Disconnect the A/C clutch.
Connect a non-powered test lamp between the power pin and ground pin at the A/C clutch vehicle harness connector.
Start engine.
Turn A/C on, wait 15 seconds.
Monitor test lamp.
After testing turn key off, remove jumper and reconnect A/C clutch and A/C cycling switch.

Does test lamp light (or can A/C clutch be heard clicking on)?

Yes	No
GO to DS22 .	For Escort/Tracer: KEY OFF. GO to Pinpoint Test Step X110 . For All Others: KEY OFF. GO to Pinpoint Test Step KM15 .

DS22 CHECK IF A SUFFICIENT A/C PRESSURE CHANGE CAN BE DETECTED BY THE ACP PID

Start engine.
A/C off.
Access ACP V PID.
Note ACP V PID voltage.
While monitoring ACP V PID voltage, turn A/C on. Five seconds after A/C clutch engagement, note voltage (if clutch does not engage, follow NO Action To Take).

Did the ACP V PID voltage change more than 0.3 volt within five seconds of clutch engagement?

Yes	No
The ACP Sensor and PCM can detect a sufficient change in A/C system pressure. For Symptom without DTC P1463: RETURN to Section 3 . All others: GO to the Climate Control System General Information, Section 414-00 in the Workshop Manual to check for proper operation of the A/C system. After any service. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	KEY OFF, A/C off. GO to DS23 .

DS23 CHECK A/C SYSTEM PRESSURE AND PRESSURE CHANGE

Install an A/C System Manifold Gauge Set and check the A/C system high pressure readings.
Start engine.
A/C off.
Note the A/C high pressure reading.
While monitoring the A/C system high pressure reading, turn the A/C on. Five seconds after clutch engagement, note the pressure (the pressure should increase).
A/C off.

Did the A/C high pressure reading change more than 207 kPa (30 psi) within five seconds of clutch engagement?

Yes	No
KEY OFF. GO to DS24 .	A/C system pressure did not change as expected. GO to the Climate Control System General Information, Section 412-00 in the Workshop Manual to check for proper mechanical operation of the A/C system. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.

DS24 CHECK VOLTAGE BETWEEN VREF AND SIG RTN TO ACP SENSOR

Disconnect ACP sensor.
Key on, engine off.
Measure voltage between VREF and SIG RTN circuits at the ACP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
KEY OFF. GO to DS25 .	VREF is out of range. KEY OFF. GO to Pinpoint Test Step C1 .

DS25 CHECK ACP CIRCUIT FOR OPEN IN SENSOR

Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.

Key off.
ACP sensor disconnected.
Disconnect PCM.
Measure resistance of ACP circuit between PCM harness connector pin and the ACP sensor harness connector.

Is resistance less than 5.0 ohms?

Yes	No
REPLACE ACP sensor. (REFER to the Climate Control System General Information, Section 412-00 in the Workshop Manual.) START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.	REPAIR open circuit. START engine. TURN A/C on, WAIT 15 seconds then TURN A/C off. RERUN Quick Test.