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JamesH
JamesH, Auto Service Tech
Category: Cadillac
Satisfied Customers: 663
Experience:  Auto Service Tech Hands On Cadillac Experience
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cadillac: SOME CODES I NEED READ THEY ARE e27 e40 e52 e90 e91 and f48

Customer Question

I HAVE A CADILAC SEDAN DEVILLE AND I HAVE SOME CODES I NEED READ THEY ARE E27 E40 E52 E90 E91 AND F48
Submitted: 7 years ago.
Category: Cadillac
Expert:  JamesH replied 7 years ago.
E27 Open throttle switch circuit, E40 Power steering pressure switch problem, E52 ECM memory reset, E90 VCC brake switch imput problem, E91 Park neutral switch problem, F48 egr control problem
Customer: replied 7 years ago.
what is a open throttle switch circuit and what can i do to correct? what is ECM memory reset what do i have to do to correct it ? EGR control promblem is that the EGR valve itself and should i replace or can i clean it?
Expert:  JamesH replied 7 years ago.
what is the year of the car?
Customer: replied 7 years ago.

1993 cadilacsedan deville

Expert:  JamesH replied 7 years ago.
Resetting the PCM

Stored fault codes may be erased from memory at any time by removing power from the PCM for at least 30 seconds. It may be necessary to clear stored codes during diagnosis to check for any recurrence during a test drive, but the stored codes must be written down when retrieved. The codes may still be required for subsequent troubleshooting. Whenever a repair is complete, the stored codes must be erased and the vehicle test driven to confirm correct operation and repair.
WARNING
The ignition switch must be OFF any time power is disconnected or restored to the PCM. Severe damage may result if this precaution is not observed.

Depending on the electrical distribution of the particular vehicle, power to the PCM may be disconnected by removing the PCM fuse in the fusebox, disconnecting the in-line fuse holder near the positive battery terminal or disconnecting the PCM power lead at the battery terminal. Disconnecting the negative battery cable to clear codes is not recommended as this will also clear other memory data in the vehicle such as radio presets.

Expert:  JamesH replied 7 years ago.
I would reset the computer first and see what codes stick as some maybe stored from a one time issue. The EGR system has to be tested by a pressure test

OPERATION



The Exhaust Gas Recirculation (EGR) system is used in an automotive engine to decrease the emission levels of oxides of nitrogen (NOx). NOx defines a group of chemical compounds containing nitrogen and varying amounts of oxygen that can have harmful environmental effects in large quantities.

NOx forms during the combustion process in amounts that is dependent on the concentration of oxygen in the combustion chamber and the duration that the combustion process temperatures exceed 1500°F. Decreased NOx levels are accomplished by reducing the peak combustion temperature through dilution of the incoming air/fuel charge with exhaust. During combustion, exhaust gas (largely non-reactive carbon dioxide and water vapor) acts to absorb a portion of the combustion energy, resulting in lower temperatures throughout the combustion process yielding lower amounts of NOx.

Desired amounts of EGR depend upon geometry of the combustion chamber and the operating condition of the engine. Extensive laboratory and vehicle tests are used to determine optimal EGR rates for all operating conditions. Too little EGR can yield high NOx, while too much EGR can disrupt combustion events.

COMPONENT TESTING



Early Model Engines

The EGR valve is opened by vacuum to allow exhaust gases to flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. The Powertrain Control Module (PCM) controls the vacuum to the EGR valve with a solenoid valve. A constant 12 volts is supplied to the positive terminal on the EGR valve. The vacuum supply to the EGR valve is regulated by the PCM controlling the EGR solenoid ground. The percentage that the PCM grounds the EGR solenoid is called the duty cycle. The duty cycle is the time the solenoid is on divided by the time it is off. A de-energized solenoid allows vacuum to pass to the EGR valve. A duty cycle of 100 percent will turn the EGR full off since the solenoid will be energized and not allow vacuum to pass to the valve. The EGR pulse width is regulated by the PCM depending on engine load conditions. When the engine is cold, within specified load range and above a specified rpm, the PCM sends 100 percent duty cycle to the solenoid and blocks vacuum to the EGR valve. When the engine is warm, the PCM sends a duty cycle to the solenoid to allow EGR.

These engine use a positive backpressure EGR valve, which requires exhaust backpressure (proportional to engine flow) to open and allow exhaust gas to flow into the intake manifold.

The PCM uses the following sensors to control the EGR solenoid:



Coolant Temperature (CTS)
Throttle Position (TPS)
Manifold Pressure (MAP)
Manifold Air Temperature (MAT)
Throttle Switch (ISC)
RPM data from the distributor reference pulses
Vehicle Speed Sensor (VSS)

Too much EGR flow tends to weaken combustion, causing the engine to run roughly or stall. With too much EGR flow at idle, cruise speed or cold operation, any of the following conditions may occur:



Engine stalls after cold start
Engine stalls at idle after deceleration
Car surges during cruise
Rough idle

If the EGR valve should stay open due to a stuck open valve, the engine may not run.

Too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. Any of the following conditions may occur:



Spark knock
Emission test failure



Click image to see an enlarged view

Fig. Exhaust Gas Recirculation (EGR) system check-4.5L engine



Click image to see an enlarged view

Fig. Exhaust Gas Recirculation (EGR) system check-4.5L engine



Click image to see an enlarged view

Fig. Exhaust Gas Recirculation (EGR) system check-4.9L engine



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Fig. Exhaust Gas Recirculation (EGR) system check-4.9L engine

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