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vipertech763
vipertech763, automotive technician
Category: Dodge
Satisfied Customers: 1780
Experience:  gold certified, dodge viper certified
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2004 Dodge: Hemi..light came on, on the dash..brake lights

Resolved Question:

I have a 2004 Dodge Ram Hemi. The Lamp out light came on, on the dash. The brake lights on the box do not work. The third brake light does work. The 4 ways, turn signals and running lamps work. I checked the bulbs, wiring and fuses/relays. All seem good. Maybe I am missing something? I am lead to believe that the brake switch is bad but not positive. I need to find the ohms values to test it. I have read about many of the same problems but no solutions. Any help would be great. Have any of you run into this problem? If so, what was the cause?
Submitted: 5 years ago.
Category: Dodge
Expert:  vipertech763 replied 5 years ago.
Good evening, do you have access to a multimeter or test light?
Customer: replied 5 years ago.
Hello, good evening to you Sir. I do, but I am not able to really check anything right now on the truck itself. It is 10 degrees outside and I don't have a garage to work in. I have the brake switch right here though, I can test that. Do you have diagrams or anything like that that you could show me? Or do you have any other ides what it may be?
Expert:  vipertech763 replied 5 years ago.

Checking the circuit at the brake switch is where I recommend checking first. Here is the information from the service manual for testing the switch:

 

DIAGNOSIS AND TESTING - BRAKE LAMP SWITCH

The brake lamp switch can be tested with an ohmmeter. The ohmmeter is used to check continuity between the pin terminals (Brake Lamp Switch Terminal Identification).

SWITCH CIRCUIT IDENTIFICATION

  • Terminals 1 and 2: brake lamp circuit
  • Terminals 3 and 4: RWAL/ABS module and Powertrain Control Module (PCM) circuit
  • Terminals 5 and 6: speed control circuit

SWITCH CONTINUITY TEST

NOTE: Disconnect switch harness before testing switch continuity.

With switch plunger extended, attach test leads to pins 1 and 2. Replace switch if meter indicates no continuity.

With switch plunger retracted, attach test leads to pins 3 and 4. Replace switch if meter indicates no continuity.

With switch plunger retracted, attach test leads to pins 5 and 6. Replace switch if meter indicates no continuity.

 

As a reference.....terminal #6 on the brake pedal switch is the one next to the plunger.

 

OPERATION

The brake lamp switch is hard wired to the Center High Mount Stop Lamp (CHMSL) and also monitored by the Instrument Cluster for use by the brake lamp, speed control brake sensor circuits and electronic brake distribution (EBD). The brake lamp circuit is open until the plunger is depressed. The speed control and brake sensor circuits are closed until the plunger is depressed. When the brake lamp switch transitions, the CHMSL transitions and instrument cluster transmits a brake applied/released message on the bus. The Integrated Power Module (IPM) will then transition the brake lamps.

When the brake light switch is activated, the Powertrain Control Module (PCM) receives an input indicating that the brakes are being applied. After receiving this input, the PCM maintains idle speed to a scheduled rpm through control of the Idle Air Control (IAC) motor. The brake switch input is also used to disable vent and vacuum solenoid output signals to the speed control servo.

Vehicles equipped with the speed control option use a dual function brake lamp switch. The PCM monitors the state of the dual function brake lamp switch.

The brake switch is equipped with three sets of contacts, one normally open and the other two normally closed (brakes disengaged). The PCM sends a 12 volt signal to one of the normally closed contacts in the brake switch, which is returned to the PCM as a brake switch state signal. With the contacts closed, the 12 volt signal is pulled to ground causing the signal to go low. The low voltage signal, monitored by the PCM, indicates that the brakes are not applied. When the brakes are applied, the contacts open, causing the PCM's output brake signal to go high, disengaging the speed control, cutting off PCM power to the speed control solenoids.

The second set of normally closed contacts supplies 12 volts from the PCM any time speed control is turned on. Through the brake switch, voltage is routed to the speed control servo solenoids. The speed control solenoids (vacuum, vent and dump) are provided this voltage any time the speed control is ON and the brakes are disengaged.

When the driver applies the brakes, the contacts open and voltage is interrupted to the solenoids. The normally open contacts are fed battery voltage. When the brakes are applied, battery voltage is supplied to the brake lamps.

The brake lamp switch can only be adjusted once. That is at the initial installation of the switch. If the switch is not adjusted properly or has been removed, a new switch must be installed and adjusted.

 

 

If the third brake lamp works then the circuit for the brake switch will check okay. As it mentioned above.....the switch also sends the brake pedal switch to the cluster which then sends it to the integrated power module (fuse box under the hood) which then turns the bed mounted brake lamps on. The bed mounted brake lamps are wired directly to the integrated power module.

 

The most likely cause will be the integrated power module. To be 100% sure....a scanner will be needed that can access the integrated power module to see if any codes and also if the lights can be actuated.

 

 

 

 

 

Customer: replied 5 years ago.
If you have diagrams I can check my truck out first thing in the morning. I propped the brake peddle and checked for power at the tail light. I was using a power probe to check for power at the pins, not probing the wires at all. The power was erratic, the light was not solid and no audible signal. I then went to a plug at the firewall, same thing there. Do you think it could be the I.P.M. (Integrated power module). How would I check that or know if it was that? Do you really need a scanner? That does not seem like it would be the cause. The truck only has 53,000 miles on it, in great shape and was a southern truck. What is the cost of the I.P.M. approx?
Expert:  vipertech763 replied 5 years ago.

The IPM has a computer mounted to it (FCM) and one of its design benefits is fuse less circuits. When a problem is detected it can turn the circuit off. To be sure a scanner will be needed. It takes a special scanner such as the factory scanner that the dealer has. Here are some related wiring diagrams:

 

graphic

 

graphic

 

Please for give me if I give you more info but the different year models have different systems. This is the older version with the seperate FCM that is mounted to it, newer year models have a fuse box/computer in one unit call the TIPM. All you can do at this point is follow the wiring back to the IPM to see if the FCM is sending out the bed mounted brake lamp voltage.

 

Here is the basic break down.......from the brake switch to the instrument cluster to the IPM then internally to the FCM and then out to the brake lamps unit mounted on the bed.

 

Expert:  vipertech763 replied 5 years ago.

Im doing a follow up and noticed that you havent replied back or ACCEPT the answer to your question yet. Please reply back if you need additional help or press ACCEPT so that the question may be closed out. Keep in mind that the experts on this site are compensated for their time spent helping customers once ACCEPT is selected. Thanks again for using Just Answer.

Customer: replied 5 years ago.
I still have yet to find the problem. With the information provided I have not been able to diagnose the actual problem. I tested the brake switch, it is good. Now I am trying to find info on the IPM and FCM. I want to find the pin locations so I can test the output voltages and anything else required. Do you have any schematics for my actual vehicle? Thanks, XXXXX XXXXX not by any means trying to avoid paying. I want the help and professional advice that was supposed to be supplied. Your information so far has been helpful.
Expert:  vipertech763 replied 5 years ago.

The schematics I gave you are for your vehicle. They are directly from Dodge. You can check the signal from the brake switch to the cluster however the cluster sends a message over the communication circuit that you will not be able to see with a mutimeter. Then you can check the output from the FCM as soon in the previous wiring diagram. In the wiring diagram with the brake switch you will see a splice which is where the circuit branches out to other directions. That splice is S214. In this next diagram you will see the same splice S214 going to the cluster. This is the circuit I mentioned that goes from the brake switch to the cluster.

 

graphic

 

You would need to remove the cluster and gain access to the white and tan striped wire and see if 12 volts is present when the brake pedal is depressed. Up to this point you will be able to check it. When it goes from the cluster to the FCM it is all computer language on the communication ciruits (one module talking to another).

 

You have the wiring diagram already for the FCM to the taillamp. If the system was working properly then you would have 12 volts coming out of the FCM on dark green and white striped wire leading to the left rear taillamp.

 

Here is the pinout for the FCM :

 

graphic

Here is the connector C3 of the IPM where the signal from the FCM leaves the IPM leading out to the left rear brake lamp:

 

graphic

INTEGRATED POWER MODULE C3 - 16 WAY

CAVCIRCUITFUNCTION
1W10 20BRWASHER PUMP MOTOR CONTROL
2L62 18WT/YLRIGHT REAR TURN LAMP DRIVER
3Z117 18BK/WTGROUND
4G31 20VT/LG (EXCEPT NGC)AAT SIGNAL
5Z118 18BK/YLGROUND
6L1 18WT/LGBACKUP LAMP FEED
7--
8--
9--
10D25 20VT/PKPCI BUS
11--
12L61 18WT/LGLEFT FRONT TURN LAMP DRIVER
13L53 18DG/WTLEFT STOP LAMP FEED
14L63 18WT/DGLEFT REAR TURN LAMP DRIVER
15L60 18WT/TNRIGHT FRONT TURN LAMP DRIVER
16G180 20VT/YL (EXCEPT NGC)SENSOR GROUND

 

So you can check the beginning ( from switch to the cluster), you cant check the portion from the cluster to the FCM, and you can check the end which is from the FCM to the left rear brake lamp bulb.

 

There will be only so much that you can check with a multimeter or power probe.....sooner or later you will need the proper scanner.

 

 

vipertech763, automotive technician
Category: Dodge
Satisfied Customers: 1780
Experience: gold certified, dodge viper certified
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