code 31
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Senior User
Joined: Oct 2005
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the plenum was not leaking. EGR and 02 sensor checked out good. I replaced plugs, wires, cap/rotor with motorcraft and all is well. Its like a new truck. Currently seeking cause of code 12 for idle.
Posting Guru
Joined: Mar 2002
Posts: 1,942
Likes: 3
From: Willamette Valley, Oregon
I dont have a 1990 manual but the 1992 manual says that code 12 is referring to the Idle Speed Control Soleniod
KE1 SERVICE CODE 12/412, 16: CHECK FOR RPM DROP
Service Code 12/412 indicates that during Engine Running Self-Test, engine rpm could not be controlled within the Self-Test upper limit band.
Service Code 16 indicates that during Engine Running Self-Test, engine rpm was too low to perform the HEGO test.
Possible causes:
-- Open or shorted circuit
-- Throttle linkage binding
-- Improper idle airflow set
-- Throttle body/ISC solenoid contamination
-- Items external to Idle Speed Control system that could affect engine rpm.
-- Damaged ISC solenoid
-- Damaged processor
l Key off.
l Connect engine tachometer.
l Start engine.
l Disconnect ISC harness connector.
l Does rpm drop or stall?
Yes
GO to «KE2».
No
GO to «KE3».
KE2 CHECK FOR EGR CODES
l Are Service Codes 31/327, 32/326/328, 33/332, 34/336/334 or 213 present?
Yes
RECONNECT ISC solenoid. GO to Quick Test Step «6.0»(2-Digit Service Codes)
or «7.0» (3-Digit Service Codes) for appropriate Pinpoint Test.
No
GO to «KE3».
KE4 MEASURE ISC SOLENOID RESISTANCE
l Key off.
l ISC solenoid disconnected.
l Measure solenoid resistance.
NOTE:
Due to diode in solenoid, place DVOM(+) lead on VPWR pin and (-) lead on ISC pin.
l Is resistance between 6.0 and 13.0 ohms?
Yes
GO to «KE5».
No
REPLACE ISC solenoid. RERUN «Quick Test».
KE5 CHECK FOR INTERNAL SHORT TO ISC SOLENOID CASE
l Key off.
l ISC solenoid disconnected.
l Measure resistance from either ISC solenoid pin to ISC housing.
l Is resistance greater than 10,000 ohms?
Yes
GO to «KE6».
No
REPLACE ISC solenoid. RERUN «Quick Test».
KE6 CHECK VPWR CIRCUIT VOLTAGE
l Key on, engine off.
l ISC solenoid disconnected.
l Measure voltage between VPWR circuit at the ISC solenoid vehicle harness connector and battery ground.
l Is voltage greater than 10.5 volts?
Yes
GO to «KE7».
No
SERVICE open circuit. RERUN «Quick Test».
The rest of these tests refer to using a Ford Breakout box which I am sure you and your mechanic do not have access to. I hope this helps you.
KE1 SERVICE CODE 12/412, 16: CHECK FOR RPM DROP
Service Code 12/412 indicates that during Engine Running Self-Test, engine rpm could not be controlled within the Self-Test upper limit band.
Service Code 16 indicates that during Engine Running Self-Test, engine rpm was too low to perform the HEGO test.
Possible causes:
-- Open or shorted circuit
-- Throttle linkage binding
-- Improper idle airflow set
-- Throttle body/ISC solenoid contamination
-- Items external to Idle Speed Control system that could affect engine rpm.
-- Damaged ISC solenoid
-- Damaged processor
l Key off.
l Connect engine tachometer.
l Start engine.
l Disconnect ISC harness connector.
l Does rpm drop or stall?
Yes
GO to «KE2».
No
GO to «KE3».
KE2 CHECK FOR EGR CODES
l Are Service Codes 31/327, 32/326/328, 33/332, 34/336/334 or 213 present?
Yes
RECONNECT ISC solenoid. GO to Quick Test Step «6.0»(2-Digit Service Codes)
or «7.0» (3-Digit Service Codes) for appropriate Pinpoint Test.
No
GO to «KE3».
KE4 MEASURE ISC SOLENOID RESISTANCE
l Key off.
l ISC solenoid disconnected.
l Measure solenoid resistance.
NOTE:
Due to diode in solenoid, place DVOM(+) lead on VPWR pin and (-) lead on ISC pin.
l Is resistance between 6.0 and 13.0 ohms?
Yes
GO to «KE5».
No
REPLACE ISC solenoid. RERUN «Quick Test».
KE5 CHECK FOR INTERNAL SHORT TO ISC SOLENOID CASE
l Key off.
l ISC solenoid disconnected.
l Measure resistance from either ISC solenoid pin to ISC housing.
l Is resistance greater than 10,000 ohms?
Yes
GO to «KE6».
No
REPLACE ISC solenoid. RERUN «Quick Test».
KE6 CHECK VPWR CIRCUIT VOLTAGE
l Key on, engine off.
l ISC solenoid disconnected.
l Measure voltage between VPWR circuit at the ISC solenoid vehicle harness connector and battery ground.
l Is voltage greater than 10.5 volts?
Yes
GO to «KE7».
No
SERVICE open circuit. RERUN «Quick Test».
The rest of these tests refer to using a Ford Breakout box which I am sure you and your mechanic do not have access to. I hope this helps you.
Posting Guru
Joined: Mar 2002
Posts: 1,942
Likes: 3
From: Willamette Valley, Oregon
Description
The Idle Speed Control (ISC) solenoid is used to control engine idle speed and dashpot functions. The ISC solenoid is mounted on the throttle body and allows air to bypass the throttle plate. The amount of air allowed to bypass is determined by the processor and controlled by a duty cycle signal.
The Idle Speed Control (ISC) solenoid is used to control engine idle speed and dashpot functions. The ISC solenoid is mounted on the throttle body and allows air to bypass the throttle plate. The amount of air allowed to bypass is determined by the processor and controlled by a duty cycle signal.
