1999 Cadillac DeVille - Answered Questions & Fixed issues

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 | 3,150 views

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.


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1999 Cadillac... | Answered on Apr 25, 2018 | 60 views

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 | 39 views

bad temp sensor or wiring harness issue.

1999 Cadillac... | Answered on Dec 31, 2017 | 117 views

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

1999 Cadillac... | Answered on Dec 28, 2017 | 73 views

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 | 38 views

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 | 119 views

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 | 140 views

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 | 154 views

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 | 87 views

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 | 77 views

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 | 82 views

The "mechanic" failed to complete the repair correctly.

1999 Cadillac... | Answered on Jul 19, 2017 | 111 views

You may have an air lock in the system. This is a pain with these engines, and Cadillac has a specific procedure for removing them (see Alldatadiy.com). Otherwise, your water pump may be shot, or there is a blockage somewhere in the cooling system (are you absolutely sure the thermostat is working - installed the right way?).
Also, are both the radiator fans running when it starts to overheat? If not, may have a blown fuse, or the relay for the fans may be shot.
All car manufacturers strongly recommend using an all-type antifreeze because it also contains corrosion inhibitors - tap water alone is not a good idea.

Most good battery chargers will trickle charge a charged battery - this is normal. Even with the car shut off, there will be a small drain on the battery to keep the electronics alive. HOWEVER, for this same reason, it is never a good idea to use a battery charger while the battery is in the car, or to jump start a dead battery in the car - the electronics do not like this.

1999 Cadillac... | Answered on Jun 18, 2017 | 103 views

Logically, if there is power at the solenoid all the time there is a problem with the brake switch assembly or wiring. If not, the solenoid may simply be stuck in the activated position.

1999 Cadillac... | Answered on Jun 02, 2017 | 158 views

Diagnostic Aids
• It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction.
• An intermittent malfunction can be caused by poor connections, broken insulation, or a wire that is broken inside the insulation.
• If an intermittent malfunction exists, refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

Do you know how to do automotive electrical wiring trouble shooting ? Use a DVOM - digital volt ohm meter ? How to use a wiring diagram to pin point testing spots in a electrical circuit ? Testing before replacing parts is key !

1999 Cadillac... | Answered on May 28, 2017 | 237 views

Could be that the hvac control module has an intermittent problem or the air mix door control for the passenger side is sticking. Check for error codes (DTCs) using a code scanner, but may not show an intermittent mechanical issue. If you can get at the air mix control on the hvac box under the dash on the passenger side, you may be able to check its operation.

1999 Cadillac... | Answered on May 25, 2017 | 57 views

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