How Dodge's Truck Lighting, Wiper System Works

Posted 1/5/2009
By Greg Montero, AAM

Dodge truck lighting and wiper systems have been in use since 2002 on full-size pickup trucks. Dodge refers to this body code as the "DR" trucks. On this system, the instrument cluster can be considered the body control module (BCM), similar to passenger cars. It is also referred to as the cabin compartment node (CCN), mechanical instrument cluster (MIC) or the electro-mechanical (EMIC) cluster. For the purpose of this article, it will be referred to as a CCN.

"Dodge truck lighting and wiper systems have been in use since 2002 on full-size pickup trucks ... On this system, the instrument cluster can be considered the body control module (BCM), similar to passenger cars. It is also referred to as the cabin compartment node (CCN)."

Dodge calls the CCN a "smart cluster" because it receives data from other modules, processes the information and displays it. For example, vehicle speed is received over the bus network from the powertrain control module (PCM) and is processed and displayed by the CCN.

When the vehicle is built in the factory and is operated initially, the vehicle identification number (VIN) is electronically burned into it. The CCN also stores the official mileage for the vehicle. If the CCN has to be replaced, the replacement CCN must be ordered with the correct VIN and mileage. Fault codes can be set by swapping in used parts such as the PCM or the CCN.

The headlamp and multifunction switches are hardwired to the CCN. The headlamp switch receives a 5-volt reference voltage from the CCN. The CCN can determine the position of the headlight switch based on this multiplexed (MUX) voltage signal. The CCN diagnoses the turn signal and hazard input circuits using a diagnostic resistor and provides diagnostics for the headlamp switch circuit. If the CCN detects a fault in the headlamp switch circuit, it turns on the exterior lights as a default and sets a diagnostic trouble code (DTC).

The front control module (FCM) receives sensed, switched and bussed inputs. It controls the power distribution to numerous circuits by using various drivers.

• High-side drivers (HSDs) switch power to a circuit.

• Relay drivers switch the control side of a relay to ground.

• Push-pull drivers switch power or ground to a circuit, depending on requirement.

The FCM monitors input and output circuits for faults and can send bus messages to other modules based on switched and sensed inputs. The FCM has drivers with self-diagnostic capabilities that can sense a short circuit or an open circuit. In the case of a short circuit, the driver can take the place of a fuse, sense an increase in current to an excessive level, store a DTC and cut off power before wiring is damaged. The driver resets automatically when the short circuit is repaired. Some drivers can defend against short circuits and low-resistance problems. They may be equipped with temperature sensing that reports the junction temperature to the microprocessor in the FCM. If a slower-acting resistive short causes the temperature to rise above 300 degrees Fahrenheit, the driver shuts off and a code is stored.

As an example, the HSDs that operate the exterior lamps can detect an open circuit in the "off" state of the driver. The driver sends the feedback voltage to the microprocessor when the driver is off. A diagnostic voltage is then sent through the circuit. Low voltage indicates a normal circuit. High voltage indicates an open or high-resistance circuit. If a fault is detected, the FCM stores a DTC, making diagnostics easier.

The FCM uses HSDs to control headlamps, turn signals, backup lamps, brake lamps and washer pumps.

The FCM uses relay drivers to control fog lamp relay, horn relay, park lamp relay, trailer stop/turn signal relays (left and right), windshield wiper high/low relay and windshield wiper "on" relay.

The trailer stop/turn signal relays (left and right) are mounted on the circuit board and can't be changed separately. If they fail, the entire power distribution center (PDC) must be replaced. The PDC is often referred to as the integrated power module (IPM) in service information because the FCM mounts to the PDC, becoming "integrated." The FCM can be serviced separately from the PDC.

When the headlight switch is turned on, the CCN interprets this MUX voltage signal and then sends a bus message to the FCM. The FCM, in turn, operates the HSDs, which operate the headlights.

Likewise, to operate the windshield wipers, the CCN monitors the MUX voltage from the multifunction switch for front wiper and washer operation. Based on the MUX voltage, the CCN sends a status message to the FCM to request the operation. The FCM, in turn, controls the "on" wiper relay and the "high/low" relay to supply the wiper motor battery voltage.

Hopefully, a little background on this will help in understanding the operation of this vehicle's lighting and wiper system.

Jim Watson is an IDENTIFIX GM specialist. He is ASE master and L1 certified.

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