Circuit Testing Procedures - Non-Dtc-Based Diagnostics: Overview Dodge Dart PF

THEORY OF OPERATION

The purpose of the following procedure is to demonstrate how to check the operation of a generic ground circuit with a test light.

Note. The circuit shown is an example, and is intended for demonstrational purpose only.

The following are circuit tests covered in this procedure

1. Testing Ground Circuit With Test Light

Note. Perform the following test using a known good test light.

The purpose of the following procedure is to demonstrate how to check for a short circuit between multiple circuits.

Note. The circuit shown is an example, and is intended for demonstrational purpose only.

The following are circuit tests covered in this procedure

1. Testing For A Short Between Multiple Circuits

Note. Perform the following test using a known good multimeter.

Below is a list of possible causes that could be related to a Multiple Short condition.

The purpose of the following procedure is to demonstrate how to check the resistance of a circuit with an ohmmeter.

Note. The circuit shown is an example, and is intended for demonstrational purpose only.

The following are circuit tests covered in this procedure

1. Testing For An Open Circuit Using An Ohmmeter

Note. Perform the following test using a known good multimeter.

Below is a list of possible causes that could be related to an Open Circuit condition.

What is current draw?

Current draw, or parasitic draw is an electrical load that draws current from the battery when the ignition is turned off. Some are considered normal, some above normal. Normal draw comes from various electronic devices connected to battery positive at all times. Many vehicle modules draw a few mA (milliamps) as a means to "Keep Alive Memory". Whether it's the clock in the radio or the last known position of the memory mirrors, these tiny amounts of current typically will only add up to 20 or 30 mA. The vehicle can sit parked for days, even a few weeks without any problems of excessive battery drain that might prevent starting. As long as the vehicle is driven periodically in order for the alternator to recharge the battery there is no problem. A problem may occur, in situations such as new vehicles in dealer stock or long term airport parking situations.

Below are some examples of modules and components that require keep alive memory

1. Powertrain Control Module (PCM)
2. Body Control Module (BCM)
3. Memory Seat Module (MSM)
4. Radio

What is excessive current draw?

Excessive current draw can be determined by an ammeter reading in excess of 50 mA. The typical "normal" current draw will not exceed 20 or 30 mA.

How to locate the problem?

Locating the problem involves a process of elimination. If the problem is not obvious, like the trunk light staying on, you will have to start troubleshooting

1. Start by removing one fuse at a time until you see the reading on the meter drop off (be careful to reinstall the fuses in their proper location).
2. Once you've determined the high-draw circuit, there still may be a half-dozen loads, each individually drawing current from the battery.
3. To zero in on that circuit or circuits, use the schematic diagram and disconnect each device on the circuit one-at-a-time and check the meter.
4. When the milliamp reading drops off significantly, you've found the problem.

Perform the following test to determine where the cause of the draw is located.

A circuit load test can be performed to test the ability of a circuit to carry the current required to operate a connected device. A circuit load test should be performed after a circuit has passed a resistance test using a DVOM and the circuit is still suspected of a failure.

1. A single copper wire strand will carry enough current to light a test light bulb, while showing very low resistance using a DVOM.
2. Some test lights are insufficient for load testing because of the very low resistance bulb being used.
3. The Load Test tool listed below will require higher current flow to power the bulb; and this will test the ability of the circuit to carry a load.
4. This test will indicate if the circuit being tested can carry the current required to operate a connected device.

Note. Depending upon the location of the circuit in question, this test may require jumper wires.

Note. Use the wiring diagrams as a guide to trace the circuits and look for any in-line connectors where the circuit failure could occur intermittently. Look for any chafed, pierced, pinched, or partially broken wires. Look for broken, bent, pushed out or corroded terminals - clean/repair as necessary. Verify that there is good pin to terminal contact in the related wire harness connectors.

Scheme 11

Here is an example of a simple tool you can build to test a circuit`s ability to carry a load.

Scheme 12

The following is a list of components required to build a load test tool

1. 3156 Bulb
2. 3156 Bulb socket
3. Negative alligator clip with covers
4. Positive alligator clip with covers
5. 2 Amp mini fuse
6. Mini fuse holder
7. 2' to 4' of Black 16ga wire
8. 2' to 4' of Red 16ga wire
9. Approved back probe tool
10. Shrink tubing
11. Solder

Voltage drop is the reduction in voltage in an electrical circuit between the voltage source and load components. The wires and connectors of a circuit should contain almost no resistance and all the voltage should be consumed through the load. The "load" is the component using the power, such as a light, starter, or blower motor. If a circuit has excessive resistance, it prevents the wire from carrying sufficient current under high load conditions. A voltage drop test is an effective way to locate excessive resistance in connections and circuits.

To preform a voltage drop test, a Digital Volt Ohm Meter (DVOM) is used to measure the voltage drop across a live circuit or connection while it is under the load. If the circuit or connection being tested has excessive resistance, the DVOM will measure the voltage that the resistance is using. Little or no voltage drop should be read, ideally less than 0.2 of a volt , anything greater indicates excessive resistance and the circuit or connection should be inspected for cleaning or repair.