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Low voltage conditions or the integrity of an electrical connection can pose some challenging events for the technician attempting to make an accurate diagnosis. In the world of automotive diagnostics, electrical problems have proven to be the most challenging, especially intermittent problems. Intermittent performance problems can be affected by connection-relate conditions and the presence of heat, cold or vibration. Imagine trying to diagnose a symptom that occurred for a millisecond yesterday on a cold morning while crossing a railroad crossing. Resistance in the vehicle’s electrical system can really make life miserable for the technician trying to identify the culprit. These are real world conditions that technicians must deal with on a weekly basis. Keeping a positive diagnostic approach is imperative in making an accurate diagnosis. It is easy to fall into a pattern of blaming an electronic component and needlessly replacing a part that may not fix the problem. However, there will be times that call for trying a known good component, as it is written in some of the diagnostic flow charts provided by the vehicle manufacturers. This should be a last step approach, as electronic components can be expensive with no return privilege.
Early on in my automotive training my instructor constantly drilled into us the importance of starting at the source of power when diagnosing electrical concerns. This would include the condition of the battery, related wiring, and connections. Never rule out the ground side of a circuit. Many electrical components get replaced when the symptom was related to an electrical connection or a low voltage condition. This can be a challenge as we must now factor in parasitic current drains to the diagnostic process, which are part of today’s technology necessary to keep computers/memories alive. A minor voltage drop can wreak havoc with today’s electronic systems. Let’s consider some of the challenges the technician must deal with on a weekly basis:
Sulfation contributes to up to 80% of all battery failures. This sulfation event occurs when the battery drops below its full state of charge for extended periods of time. During this low state of charge, lead sulfate crystals form on the negative plates. These deposits result in a reduction of the available surface of the battery’s active material, causing a reduction of the capacity of the battery. The presence of the sulfation prevents the battery from accepting a full state of charge.
Conditions That Promote Sulfation:
1) Reduced electrolyte level due to gassing, spillage or leakage.
2) Cold weather conditions resulting in increased starter amperage draw due to a thicker oil viscosity.
3) Low state of charge due to an electrical problem such as a defective alternator, or conditions resulting in excessive electrical demands. This often occurs when vehicles are operated in heavy traffi c conditions, short trip driven vehicles, and vehicles driven at slow speeds during periods of high electrical demand, preventing the alternator from keeping up with the demand.
4) Temperatures exceeding 100° F can promote an increased discharge rate. This is a problem, considering the tight underhood quarters, high underhood temperatures and batteries positioned out of the airﬂ ow. Some of the newer vehicles incorporate a wrap/blanket positioned around the battery for heat reduction.
5) Vehicles not driven on a daily basis. This includes vehicles that may sit for long periods of time on a car lot, or collector cars that are seldom driven farther than to a water hose for clean-up and then parked.
6) Parasitic current drains.
With today’s systems, little or no warning may be given until a no-start condition occurs. There are several reasons for this symptom. High heat is the number one battery killer. High underhood temperatures, a 90-plus degree day and tight battery mounting quarters all contribute to overheating and premature battery failure. Excessive heat causes gassing, resulting in electrolyte loss, plate corrosion and internal shorts. In extreme heat conditions, the average battery life is 36 months. Cold weather requires a heavy amperage draw to start a cold engine with thick oil, plus a battery is less efficient at colder temperatures.
Some current drain on the battery should be considered a normal characteristic. This condition is referred to as parasitic current drain and is necessary to keep accessory devices and computer memories alive when the key is in the off position. The electrical drain is usually in the 30 ma range to a maximum of 50 ma on some vehicles equipped with highly optioned electrical accessories. This minute current drain is not a problem on vehicles that are driven daily and at speeds above 1,000 RPM. It can pose a problem when vehicles are not driven for periods of 3-4 weeks. During this lay-up time the battery may become discharged to a level that a no-start condition may be encountered. In addition, the vehicle may encounter some difficult-to-diagnose electrical symptoms. When testing for parasitic current drain, be aware that when the battery is initially connected you may observe a 9-10 amp draw for a few seconds, as the computers and capacitors power up, and this is referred to as the initialization period. Follow the vehicle manufacturer’s specifications for parasitic current drain, as some applications may have unique initialization periods. For example, some GM trucks and SUVs equipped with Dual Zone AC require up to four hours for the control head to go to sleep, and this is considered a normal characteristic. This variance can lead to a misdiagnosis. Conditions like this are usually noted in a tech service bulletin from the vehicle manufacturer. Make certain you review the service bulletins before investing a lot of diagnostic time chasing a condition that may be a normal characteristic for the application or a condition for which a factory solution is offered.
Intermittent symptoms are the most frustrating and labor consuming diagnostic exercises, even for the most experienced technician. Intermittent electrical connections are one issue and resistance values of a connection is another concern. High resistance within a connection can result in diagnostic trouble codes (DTCs) being set. In some circuits modules compare electrical values to determine the proper operation of a module or circuit. Resistance values that can vary in milliohms may result in DTCs being stored, leading the technician down a different path of diagnostics, often needlessly replacing an electronic module. These variances in resistance values are not measurable with a common volt/ohm meter.
When diagnosing an intermittent electrical concern, the integrity of the electrical connections should be a first concern. Often, a symptom is resolved by disconnecting and reconnecting an electrical connector. The integrity of a terminal/connection should be checked by using the proper terminal size test tool or a like mating terminal to determine if the connection establishes good electrical contact.
The accumulation of an oxidized debris referred to as terminal fretting corrosion may occur between two electrical contact surfaces within an electrical connector. This condition occurs due to poor terminal retention/poor connection, vibration and thermal cycling. This often occurs due to a connector or wiring harness that is not properly secured, resulting in constant movement. Visually, fretting corrosion may have the appearance of dark smudges on the terminals where electrical contact has been made.
When these conditions occur on low current circuits, the resistance may promote intermittent performance symptoms that are difficult to pinpoint. On higher current circuits, a permanent increase in resistance may result in total/permanent circuit failure. Any number of modules on the vehicle can be affected. The symptoms may include a No Start/No Crank condition, MIL lamp illumination, multiple codes stored, etc. The intermittent symptoms are the most difficult to duplicate, making the diagnostic efforts challenging.
Clean, tight connections are imperative. Once this has been established, a light coating of dielectric lubricant applied to the terminals is recommended. Do not pack the connectors with the lubricant as an excessive amount may result in a hydrolock condition, preventing full terminal engagement when mating the connectors. A light coating with a small brush is all that is necessary to prevent the fretting condition.
Summary: Intermittent conditions are the most challenging but the most rewarding, especially when your diagnostic efforts succeed where others have given up or refused to tackle the problem.View PDF