1981-1985 Cadillac Information

Information and specifications related to the 1977-1985 full-size, body-on-frame, rear wheel drive, Cadillac models manufactured by General Motors (GM) in Detroit, Michigan, USA.

Cadillac Reviews

Read the Consumer Guide review of the 1981 Cadillac lineup here.

TROUBLE CODE DIAGNOSIS

The following abbreviations will be used in this section:

TPS	-	Throttle Position Sensor
ECM	-	Electronic Control Module
ISC	-	Idle Speed Control
HEI	-	High Energy Ignition
MAP	-	Manifold Absolute Pressure (Sensor)
BARO	-	Barometric Pressure (Sensor)
ECC	-	Electronic Climate Control
MAT	-	Manifold Air Temperature (Sensor)
CTS	-	Coolant Temperature Sensor
MPG	-	Miles Per Gallon (Display Panel)
EGR	-	Exhaust Gas Recirculation
MD	-	Modulated Displacement
MDA	-	Modulated Displacement Amplifier

The dash mounted "CHECK ENGINE" light is used to inform the technician of detected system malfunctions or abnormalities. The light goes out automatically of the fault clears (intermittent). However, the ECM stores the trouble code associated with the detected failure until the diagnostic system, is "Cleared" or until 20 ignition switch (on-off) cycles have occurred without the fault reappearing.

Proper operation of the light is as follows:

1. The light is normally off.
2. A bulb check is preformed when the ignition is in the "On" and "Crank" positions. When the engine starts, the bulb goes out.
3. The light comes on and stays on when a constant malfunction is detected.
4. If a malfunction is intermittent, the light will go out when the malfunction is not present. The light will come on each time a malfunction is detected (may flicker).
5. The light stays on when the system is displaying the diagnostic routine.

HOW TO "ENTER" DIAGNOSTIC MODE

To enter diagnostic mode, proceed as follows:

1. Turn the ignition "ON".
2. Depress the "OFF" and "WARMER" buttons on the ECC panel simultaneously and hold until "--" appears. "88" will then be displayed which indicated the beginning of the diagnostic readout.
3. Trouble codes will be displayed on the digital ECC panel beginning with the lowest numbered code. Note that the MPG panel goes blank when the system is displaying as the diagnostic mode.

HOW TO "CLEAR" TROUBLE CODES

Trouble codes stored in the ECM's memory may be cleared (erased) by entering the diagnostic mode and then depressing the "OFF" and "HI" button simultaneously. Hold until "00" appears. After "00" is displayed the ECM will display "70". Turn the ignition off for at least 10-seconds before re-entering the diagnostic mode.

HOW TO "EXIT" DIAGNOSTIC MODE

To get out of the diagnostic mode, depress any of the ECC "function" keys (Auto, Econ, etc. except Rear Defog) or turn ignition switch off for 10 seconds. Trouble codes are not erased when this is done. The temperature setting will reappear in the display panel.

DIAGNOSIS PROCEDURE

When the check engine light turns on, it indicated that a malfunction has occurred for which a trouble code has been stored. The trouble code can be displayed on the ECC control panel. The malfunction may or may not result in abnormal engine operation.

To determine which system(s) has malfunctioned, proceed as follows:

1. Turn the ignition "ON" for 5 seconds.
2. Depress the "OFF" and "WARMER" buttons on the Electronic Climate Control panel simultaneously and hold until "--" appears.
3. The numerals "88" should then appear. The purpose of "88" is to check that all segments of the display are working. Diagnosis should not be attempted unless the entire "88" appears as this could lead to misdiagnosis (Code 31 could be Code 34 with two segments of the display inoperative, etc.).
4. If trouble codes are present, they will be displayed on the digital ECC panel as follows:
   1. The lowest numbered code will be displayed for approximately two seconds.
   2. Progressively higher numbered codes, if present will be displayed consecutively for two seconds intervals until the highest code present has been displayed.
   3. "88" is again displayed.
   4. Parts a b and C above will be repeated a second time.
   5. when the trouble codes have been displayed, code 70 will then be displayed. Code 70 indicates that the ECM id ready for the next diagnostic feature to be selected.
5. If no trouble codes are present, "88" will be displayed for a longer period of time, and then the ECM will display code 70. Code 70 indicates that the ECM is ready for the next diagnostic feature to be selected.

Engine Data Display Procedure

Code "70" must be displayed on the ECC panel before engine data can begin. To display engine data slide the cruise control instrument panel switch from the ON position to the OFF position (1982 model year cars push "RESET" button the on the MPG display) the display code will advance from "70" to "90". To display the next parameter depress the "INSTANT/AVERAGE" button on the MPG panel. When the last parameter/data is reach the display will change to "95."

Engine Data Display

Parameter No.  Parameter  Value  Units
01 TPS (Throttle Angle) XX Degrees 
02 MAP (Manifold Air Pressure) XX kPa (KiloPascals) 
03 BARO (Barometric Air Pressure) XX kPa (KiloPascals) 
04 Coolant Temperature XX 0=-40C 99=150C (Degrees Celsius) 
05 MAT (Manifold Air Temperature XX 0=-40C 99=150C (Degrees Celsius)
06 Injector Pulse Width  X.X MSec (Milliseconds)
07 O2 Sensor .XX Volts 
08 Spark Advance XX Degrees 
09 Ignition Cycles XX Key Cycles 
10 Open/Closed-Loop Indicator X 0=Open Loop 1=Closed Loop (HT4100 battery voltage)
11 Battery Voltage X.X Volts - Will Not Display 10's Digit  (HT4100 engine RPMs)
12 Vehicle Speed (HT4100)
13 Prom ID (HT4100)

On cars equiped with an "outside temperature" button on the ECC, ECM operating mode can be switched between closed loop vs. open loop mode by depressing this button. With the LED illuminated ECM operates in a "Closed Loop Mode" - with the LED off ECM is in "Open Loop Mode."

            ECM         O2      Throttlet        TCC output    4th              A/C
            operating   sensor  switch input     output        gear input       clutch
            mode        input   input                          input            output
----------------------------------------------------------------------------------------------
Light on   Closed loop  Rich    Closed throttle  TCC enabled   In 4th gear      A/C Clutch enabled
Light off  Open loop    Lean    Open throttle    TCC disabled  Not in 4th gear  A/C Clutch disabled

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