Test Procedure

WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

FC1 DTC P0A27: CHECK FOR SELF-TEST DTCS

Is TBCM DTC P0A27 present during self-test?

Yes	No
For KOEO and KOER DTC P0A27, GO to FC2.	Unable to duplicate or identify the fault at this time.
For continuous memory DTC P0A27, GO to FC7.	RETURN to SYMPTOM CHARTS for further direction.

FC2 CHECK THE BATTERY POWER OFF PID FREQUENCY

Access the PCM and monitor the BPO_Hz PID.

Is the frequency between 1.96 - 2.04 Hz?

Yes	No
GO to FC7.	GO to FC3.

FC3 CHECK THE BATTERY POWER OFF CIRCUIT FOR AN OPEN IN THE HARNESS

PCM connector disconnected.
TB-A connector disconnected.

Measure the resistance between:

( + ) PCM Connector, Harness Side	( - ) TB-A Connector, Harness Side
BPO - Pin B24	BPO - Pin 8

Is the resistance less than 5 ohms?

Yes	No
GO to FC4.	REPAIR the open circuit.

FC4 CHECK THE BATTERY POWER OFF CIRCUIT FOR A SHORT TO VOLTAGE IN THE HARNESS

Key ON, engine OFF.

Measure the voltage between:

( + ) PCM Connector, Harness Side	( - ) Vehicle Battery
BPO - Pin B24	Negative terminal

Is the voltage less than 1 V?

Yes	No
Key in OFF position. GO to FC5.	Key in OFF position. REPAIR the short circuit to PWR.

FC5 CHECK THE BATTERY POWER OFF CIRCUIT FOR A SHORT TO GROUND IN THE HARNESS

Measure the resistance between:

( + ) PCM Connector, Harness Side	( - ) Vehicle Battery
BPO - Pin B24	Negative terminal

Is the resistance greater than 10K ohms?

Yes	No
GO to FC6.	REPAIR the short circuit to GND.

FC6 CHECK THE BATTERY POWER OFF CIRCUIT INTEGRITY

PCM connector connected.
TB-A connector connected.
Isolate the BPO circuit at the TB-A connector.

Connect a 5 amp fused jumper wire between the following:

Point A TB-A Connector, Harness Side	Point B PCM Connector, Harness Side
BPO - Pin 8	MSDN - Pin T11

Key ON, engine OFF.
Access the PCM and monitor the BPO_Hz PID.

Is the PID frequency between 49 and 75 Hz?

Yes	No
Key in OFF position.	Key in OFF position.
REFER to HIGH VOLTAGE TRACTION BATTERY to continue the battery power off circuit diagnosis.	GO to FC8.

FC7 CHECK THE BATTERY POWER OFF CIRCUIT FOR AN INTERMITTENT CONCERN

PCM connector connected.
Transaxle Assembly-A connector connected.
Key ON, engine OFF.
Access the PCM and monitor the BPO_Hz PID.
Carefully wiggle all accessible wiring and connectors associated with the circuit and look for a change in the PID state.

Is a fault indicated during the wiggle test?

Yes	No
Key in OFF position.	Key in OFF position.
REPAIR as necessary.	GO to Pinpoint Test Z .

FC8 CHECK FOR CORRECT PCM OPERATION

Disconnect all the PCM connectors.
Visually inspect for:
- pushed out pins
- corrosion
Connect all the PCM connectors and make sure they seat correctly.
Carry out the PCM self-test and verify the concern is still present.

Is the concern still present?

Yes	No
INSTALL a new PCM. REFER to FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY (EEPROM) .	The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.