ECU - The Engine Control Unit governs the majority of the engine electrical operation, and is subject to failure like any electrical component. Onboard diagnostic procedures allow testing of the ECU and engine components to help with fault diagnosis. Care should be taken with any vehicle that has an ECU, as voltage spikes or electrical failures can cause irreversible damage. Jump starting is a common cause of damage, and should only be performed with quality surge protected leads.
Temperature sender unit - The temperature sender unit provides the ECU with a varying voltage, which is used to calculate fuel delivery depending on engine temperature. If the sender unit fails, and the wrong voltage is sent to the ECU, the ECU fuel delivery calculations will be incorrect, and this can lead to excessive fuel consumption. In most cases a fault code will be stored in the ECM.
Oxygen sensor - The Oxygen (O2) sensor is an exhaust probe that measures the amount of unburnt fuel in the exhaust gases. The ECU uses this sensor to trim fuel delivery and maximize efficiency. O2 sensors are a common item to fail and can cause erratic engine idle and performance. O2 sensor problems will usually store a fault code in the ECM.
DFI module and Coil pack - VR V6 commodores use a Direct Fire Ignition (DFI) module and three 2 coil packs to distribute spark instead of a conventional coil and distributor arrangement. These units can fail which will prevent the engine from starting.
VR Coil (3 required) - Part Number 10472401
VR DFI Module - Part Number 10475225
VR Coil Pack and DFI Module assembly - Part Number DFI4021M
V6 Crank angle sensor - V6 commodores use a crank angle sensor mounted behind the harmonic balancer, to send crank position information to the ECM and DFI assembly for ignition calculations. The crank angle sensor's main weakness is internal cracking. A common scenario is with a cold engine, the sensor and engine are fine, but as the engine warms up and ambient temperature increases, the crank angle sensor expands with the heat and open circuits, which results in loss if ignition. Dousing the crank angle sensor with cold water will cause it to contract and operate correctly, until it once again becomes warm. In order to replace the crank angle sensor, the harmonic balancer will need to be removed. Crank angle sensor faults will usually store a fault code in the ECM.
V6 Thermo fan - V6 engine thermo fans suffer from intermediate operation, usually caused by connection problems at the thermo fan fuse or relay. Fuse terminal melting is common, usually because of bad connections and the amount of current draw through the system. External fuse routing is usually the quickest way to bypass damaged terminals, along with thoroughly cleaned wiring connections.
Tail lamps - VR tail lamps suffer from fading reflector lenses. Problems also arise in VR tail lamps because of inadequate sealing to prevent water entry. Water entry into the tail lamps can lead to rusting globe terminals, which restricts electrical connectivity. Rectifying these problems usually requires new tail lamps and tail lamp wiring harnesses if rusted terminals are present.
Oil light - The oil sender unit on a VR commodore is responsible for the oil light, and an oil pressure signal to the ECM. Moisture contamination can cause the oil warning lamp to stay on until the moisture has dispersed. The oil sender units can also leak oil when fatigued, which causes a similar problem.
Speedo Sender - The electronic speedo sender on a VR commodore manual sends 10ppr (Pulses Per Revolution) to the ECM and the Speedo. The speedo senders can fail, which is evident when the speedo stops working, or when the speedo displays a flickering speed without the vehicle moving. VR's with automatic transmissions also rely on the speed signal for idle control during deceleration, but don't often cause problems.
Wiper mechanism - VR wiper arm mechanisms commonly break at the right mounting bracket below the front windscreen. This sometimes results in the wiper arm hitting and cracking the front windscreen. Wiper mechanisms are available from most wreckers.
Power antenna - Power antennas can develop a parking problem, i.e. they do not descend all the way, or consistently clunk during operation. Inside the power antenna mast is a plastic ribbed rope which is connected to cogs inside the power antenna motor. Either through moisture buildup inside the antenna from inadequate drainage, or plastic fatigue, the rope can break or lose teeth. New Mast and Rope assemblies are available through GMH dealers, be need to be fitted and retimed accordingly to ensure correct operation. Power antennas are controlled by a module, which is located on the left side of the dash, behind the glove box. The stereo triggers the module, and therefore the antenna will only stay up if the stereo is on. The module controls the height that the antenna will extend to, and this can be increased or decreased by the binnacle switch on the dash. The modules can be faulty, causing the antenna not to work, or to work intermittently. Modules are not all preset the same. Some may lift the antenna mast up to the limit, where as some may only lift them a few inches.
Power antenna mast and rope - Part number VS18188
Power antenna module - Part number 92029494
Erratic tacho V8 - One possible cause of an erratic tacho in a V8, is caused by the distributor cap and/or rotor button wear. The cap and rotor can become worn through age, and their conductivity is reduced. Ignition leads can also affect the life span of these components.
Distributor cap - Part number GB926 (Bosch)
Rotor - Part number GB901 (Bosch)
Electrical malfunctions - VR onwards Commodores use a body control module. This module is responsible for electrical operation of components inside the vehicle, and is also responsible for the vehicle alarm, and keyless entry systems. This module is separate from the engine computer, and governs the operation of switches and modules used by the driver. The body control module controls most power systems, such as central locking, electric windows, power antennas, window demisting and cruise control. If this module becomes faulty through a spike voltage, or an accident, any, or all of the above mentioned power systems may become inoperative. Depending on the Vehicle type, a new body control module will come with a new alarm remote. Some types are supplied without an alarm remote, and in this case, a new remote will be needed, and the car will need to be booked in for a tech 1, to reprogram the remote to the body control module.
Cruise Control - The cruise control stalk on VR's are prone to fail either through worn button contacts or broken wires at the end of the stalk. New indicator/cruise control stalks are available through GMH!
Indicator stalk with Cruise Control - Part number 92054763
Fuel pumps - The internal fuel pump requires adequate fuel for lubrication. Continuously running with very little fuel or running out of fuel can damage the pump, as there is no fuel for lubrication. If the pump is run without fuel, the heat generated can wear and seize the pump and no fuel will be delivered to the injection system. The EFI (Electronic Fuel Injection) system requires approximately 30-40 PSI to operate effectively. New pumps are readily available.
Electric fuel pumps are also a cause of engine starting problems. Sometimes the car will start, run for a while, and then stall. As the fuel pumps get older, and lose efficiency, they get hot. Eventually they seize. Sometimes, if the car is let to cool (and the pump), the car can be restarted. (A little cheat note hear in case you ever get stuck, if you can't hear the internal pump working on first ignition, tap the bottom of the fuel tank, which jars the pump, and sometimes unseizes it. You will still need to get it checked/replaced, but it may not leave you stranded.)
VR Internal Fuel Pump V6 - Part Number 6443224
VR Internal Fuel Pump V8 - Part Number 6443331