1991 Cadillac Brougham Diagnostic codes via climate control

SYMPTOM DESCRIPTION:
This section is used to determine the most likely cause of a trouble code that is stored in the ECM. The SERVICE ENGINE SOON or CHECK ENGINE light will only be ON if the malfunction exist under the conditions listed. If the malfunction clears, the light will go out and the code will then be stored. Any codes stored will be cleared if no problem reoccurs within 50 engine starts.

CODE AND CIRCUIT POSSIBLE CAUSE
CODE 13 Indicates that the oxygen sensor circuit
OPEN Oxygen Sensor (O2) circuit or sensor was open for one minute while
off idle.
CODE 14 Sets if the sensor or signal line are
Coolant Sensor (CTS) grounded for 3 seconds.

HIGH Temperature indication

CODE 15 Sets if the sensor, wires, or connections
Coolant Sensor (CTS) are open for 3 seconds.

LOW Temperature indication

CODE 21 TPS voltage of more than 2.5 volts for
Throttle Position Sensor (TPS) 3 seconds at an engine speed less than 1200 rpm.

HIGH Voltage Signal

CODE 22 A shorted to ground or open signal circuit
Throttle Position Sensor (TPS) will set code in 3 seconds.

LOW Voltage Signal

CODE 23 Sets if the sensor, wires, or connections
Manifold Air Temperature Sensor (MAT) are open for 3 seconds.

Or Intake Air Temperature (IAT)
LOW Temperature indication

CODE 24 No vehicle speed present during road
Vehicle Speed Sensor (VSS) load deceleration.

NO Vehicle Speed Indication

CODE 25 Sets if the sensor or signal line are
Manifold Air Temperature Sensor (MAT) grounded for 3 seconds.

Or Intake Air Temperature (IAT)
HIGH Temperature indication

CODE 32 Vacuum switch shorted to ground on start up
Exhaust Gas Recirculation (EGR) OR

Switch not closed after the ECM has commanded
EGR for a specified period of time.
OR
EGR solenoid circuit open for a specified
period of time.

CODE 33 MAP sensor output too high for 5 seconds
Manifold Absolute Pressure (MAP) or an open circuit.

LOW Vacuum

CODE 34 Low or no output from sensor with engine running.

Manifold Absolute Pressure (MAP)
HIGH Vacuum

CODE 35 IAC error.

Idle Air Control (IAC)

CODE 42 ECM has seen an open or grounded EST or Bypass circuit.

Electronic Spark Timing (EST)

CODE 43 Signal to the ECM has remained low for too long
Electronic Spark Control (ESC) or the system has failed a functional check.
CODE 44 If voltage to oxygen sensor remains BELOW.2v
LEAN Exhaust Indication. For more than 20 seconds, code is set.
CODE 45 If voltage to oxygen sensor remains ABOVE.7v
RICH Exhaust Indication. For more than 1 minute, code is set.
CODE 51 Faulty MEM-CAL, PROM, or ECM.
CODE 52 Faulty or missing CAL-PACK.
CODE 53 System overvoltage. Indication of a faulty alternator
or regulator. Camaro/Firebird uses a Code 53 for
Vehicle Anti-Theft System (VATS).
CODE 54 Sets when the fuel pump voltage is less than
LOW Voltage To Fuel Pump. 2 volts when reference pulses are being received.
CODE 55 Faulty ECM.

DESCRIPTION :

The Electronic Climate Control (ECC) head has the ability to display ECM trouble codes. Checking the operation of the "SERVICE ENGINE SOON" ("CHECK ENGINE") light or for a code 12 may be accomplished by grounding the ALDL terminal (A to B).

TEST DESCRIPTION : The numbers below refer to circled numbers on the diagnostic chart.

Enter the diagnostics by simultaneously pressing the ECC display panel OFF and WARMER buttons until all displays are lit.
Malfunction codes are displayed in the following sequence:
ECC Current codes (Parameter Number-00)
ECC History codes (Parameter Number-00)
ECM codes (Parameter Number-01)
To select a specific diagnostic parameter, press HI to increment the number, and LO to decrement the number.
Clearing codes returns to parameter number display.
OUTSIDE TEMP toggles display between parameter number and parameter data.
NOTE : To exit the diagnostics test, press AUTO.