Hello. Is the ABS light on as well? Does the ABS light turn on when the ignition is turned on? You said the engine is a 4.6L. This truck came with a 3.7L, 4.7L 5.7 and a 5.9L. Which one is it? Is the vehicleXXXXX Thanks.
Sorry it is 4.7L. the abs light works as it should. comes on when you start truck then goes out. It isXXXXX The sensor under the master cyl has also been checked.
I will be glad to help you out with this strange problem. Please give me some time to do some research on this situation. I will get back with you most likely in a few hours. Thank you for your patience. Some more information in the meantime would be helpful... How did you check the sensor under the master cylinder? Does the brake pedal feel spongy or unusual to you? Thanks.
pedal feels fine,sensor was checked by local shop, I don't know how it was done. They also ran the other tests and inspection of brakes.
The Instrument Cluster controls the amber antilock brake system warning indicator. All Dodge Truck Instrument Clusters have direct control over the ABS warning indicator and Brake warning indicator. The Instrument Cluster transmits a message over the PCI BUS relating to diagnostics and current lamp status for the ABS and Brake indicator. The Instrument Cluster will expect a PCI BUS message back from the CAB (Controller Antilock Brakes) indicating whether the indicator should be turned on or off. In the event that no signal is received from the CAB for a certain number of time, the Instrument Cluster will illuminate the ABS warning indicator. The indicator provides notice of ABS system-related problems and the need to take diagnostic action. Since you do not have an ABS light, you know that the PCI BUS data line is intact between the CAB and the instrument cluster. The vehicle Instrument Cluster has a red Brake warning indicator to alert the driver to the following conditions:
Level of brake fluid is low. The brake fluid level sensor has a float in it and the float can get stuck in the down position illuminating the red brake warning lamp. Filling the brake fluid and tapping on the brake fluid reservoir usually un sticks the sensor. The switch signals the CAB for a hydraulic fluid problem. The antilock system uses input from the brake fluid level switch when activated. A low brake fluid condition in the master cylinder will close the switch circuit and read 0 volts. When the brake fluid level is at specifications, the switch will open and circuit sense voltage will read 5 volts. This signal tells the CAB if there is enough brake fluid in the master cylinder to have an antilock operation. The brake fluid level switch is located in the master cylinder with 10k resistor. The switch is a Hall effect design and uses a float to determine level. The CAB sends a 5V (Gray/Black wire) signal to the sensor. If the float goes down below a certain level, the 5V signal gets grounded by the sensor (Black/DarkGreen wire) and the CAB interprets this as low brake fluid level condition. If the fluid level is determined to be good, the CAB sends a signal through Data communications (PCI BUS) to the instrument panel telling it to not illuminate the Brake warning lamp.
Parking Brake applied. The parking brake pedal has a switch that grounds out (white/LightGreen wire) when the parking brake is engaged. The sensors can get stuck and will send a ground to the instrument panel causing the brake warning lamp to illuminate. Also, if the wire from the parking brake to the instrument panel gets shorted to ground, the light will illuminate. Also, sometimes the parking brake will look like it is fully up when in fact it is slightly stuck down.
So, unplug the brake fluid level switch and if the brake light goes out, the float is stuck or the sensor is faulty. Since unplugging the switch will leave the 5V signal ungrounded, the CAB will see 5V on the signal wire and pass the brake level test.
Unplug the parking brake switch. If the light goes out, the parking brake switch is stuck and you can try to unstuck it or replace the switch. The parking brake pedal may be slightly stuck low.
If unplugging both sensors does not turn off the light, check for a shorted wire from the parking brake switch and the instrument cluster (White/LightGreen wire).
Check the level switch wiring and proper signal from CAB. Check for a grounded 5V wire (Gray/Black) from the brake fluid level sensor and the CAB. Check that the wire has a 5V signal at the brake level sensor connector unplugged. If no 5V signal, check it at the CAB. If no signal is present at the CAB and the wire is not shorted to ground, check for powers and grounds at the CAB. If good, replace the CAB.
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Tried all of the above without resolveing problem. Will let you know if someone figures it out.
Do you have a 5V signal at the brake level snsor grey/black? Did you pull the intsrument cluster and see if there is ground on the white/light green wire? Some testing will be required. You can do the testing yourself with a voltmeter and save a $90 diagnostic fee. I will be glad to walk you through this steb by step. Start with the first 2 readings I just asked for. Thanks.
Still no fix,but gave plenty of places to look. Will let you know if we ever find it.