20 Most Recent 1999 Cadillac DeVille Questions & Answers


Trouble Code: P1258 (4.6L V8 VIN 9 Auto)
Engine Metal Over-Temperature Protection
Number of Trips to Set Code: 1
OBD II Monitor Type: CCM Details
Indicators: MIL Details
Trouble Code Conditions:
DTC P0117, P0118 and P0125 not set, Engine started; and the PCM detected the ECT sensor indicated more than 270ºF for 10 seconds. The PCM uses the ECT sensor to detect if the engine is running too hot (when the ECT sensor is over 268ºF). If the engine is overheated, DTC P1258 will set. The PCM will disable 2 groups of four cylinders by turning off the fuel injectors. By switching between the two groups of cylinders, the PCM is able to reduce the temperature of the coolant and lower the temperature.

Possible Causes:
  • Engine cooling system problem (test the cooling fan operation)
  • Engine coolant level is low or the mixture is not correct
  • ECT sensor is out-of-calibration or "skewed"

1999 Cadillac... | Answered on Jan 18, 2019


Air Mix Actuator Replacement - Driver





Removal Procedure





  1. Remove the right sound insulator. Refer to Instrument Panel Insulator Panel Replacement - Right Side in Instrument Panel, Gauges and Console.


  2. Remove the instrument panel compartment. Refer to Instrument Panel Storage Compartment Replacement in Instrument Panel, Gauges and Console.


  3. Unsnap the rod from the plastic retainer on the actuator arm.

  4. Remove the two screws from the actuator (2).


  5. Disconnect the electrical connector (1).


  6. Remove the actuator (2).


  7. Inspect the air mix door for free travel.

1999 Cadillac... | Answered on Nov 19, 2018


It may be more than just your key. You may have an issue at the Theft Deterrent Module. This is something that can be bypassed, but it is a tough install.

http://www.diy-gm-security.com/

newrockies pro module-p30ovgg2scztm2rufkeeumkt-1-0.jpg

1999 Cadillac... | Answered on Apr 25, 2018


What you may be hearing is hum from a low voltage power module under the dash, which is activated every time you open a door. It should shut off after doors are closed, all timed devices (such as cabin lights) turn off and the key is not in the ignition. If your battery is in good condition, then either this module, the keep-alive module or something else drawing current is not shutting off the way it is supposed to. Start by checking for trouble codes (DTCs) with a good code reader.

1999 Cadillac... | Answered on Jan 20, 2018


bad temp sensor or wiring harness issue.

1999 Cadillac... | Answered on Dec 31, 2017


air lock in the system
have it professionally bled out at a radiator shop

1999 Cadillac... | Answered on Dec 28, 2017


Heater core sounds to be leaking but check all the hoses going to heater, could be loose and leaking into the vehicle.

I’m happy to help further over the phone at https://www.6ya.com/expert/pat_7f6b46a4565f904d

1999 Cadillac... | Answered on Dec 28, 2017


The bad news is that it is most likely a faulty actuator and this will be difficult to replace as they have to partially dismantle the dash to get at it. Go to a couple of dealers and get them to give you a quote for the work. They may not be able to give you an exact quote as they wont know exactly what the problem is until it is dismantled, so ask for an estimate. Jobs like this usually wont be expensive for parts, but there is a lot of labour involved..

1999 Cadillac... | Answered on Nov 22, 2017


The pump is back under the rear of car, but by now, the shocks are sure to be leaking, which causes the pump to run too much burning it up. Best fix is to replace rear shocks with coils and dump the self leveling feature, or prepare to pay big bucks to replace most components.

1999 Cadillac... | Answered on Oct 13, 2017


Engine Cooling Fan Relay 1
In the center front of the engine compartment, on the lower radiator support, near the cooling fans
Engine Cooling Fan Relay 2
In the center front of the engine compartment, on the lower radiator support, near the cooling fans
Engine Cooling Fan Relay 3
In the center front of the engine compartment, on the lower radiator support, near the cooling fans

1999 Cadillac... | Answered on Oct 11, 2017


Check in this order: Is the compressor starting when you turn the car on? If not: is the fuse burnt, broken wires? If not: Is the linkage that connects the frame to the left rear shock broken or seized? (more wires to check here). If the compressor runs and the linkage is functional, spray some windex (or soapy solution) on the rubbers of the rear shocks and around the hoses to see if air is bubbling out. If so, this is where the problem is. Many aftermarket shocks/struts are available (check ebay) online for as little as $ 150.00 each, and $ 175.00 for the compressor.

1999 Cadillac... | Answered on Sep 25, 2017


Computer glitch , have it checked for DTC'S - diagnostic trouble codes . Not all codes turn on the check engine light . Plus DTC'S for the BCM - body control module won't turn the check engine light on at all , could turn on a yellow wrench symbol on the insturment cluster .
Stop putting head gasket sealer into the cooling system , could clog it up.

1999 Cadillac... | Answered on Sep 13, 2017


If your key has the resistor pellet with the short wires on both sides of the shank, I can provide a bypass method. Basically, you make a small resistor of ohms equal to the key, cut the passlock wires at the bcm, and solder the resistor to the bcm side of the wires. I have done this many times.

1999 Cadillac... | Answered on Sep 03, 2017


Have the dealership call GM and get a Cadillac professional to their dealership..they CAN do it... ( I am a former GM Supplier Quality Engineer )

1999 Cadillac... | Answered on Aug 23, 2017

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