Express 1/2 Ton Van V8-5.7L VIN R (1999)
Knock Sensor: Diagnostic Aids
Basic Knowledge Required
Without a basic knowledge of electricity, it will be difficult to use the diagnostic procedures contained in this section. You should understand the basic
theory of electricity and know the meaning of voltage (volts), current (amps) and resistance (ohms). You should understand what happens in a circuit
with an open or a shorted wire. You should be able to read and understand a wiring diagram.
Checking Aftermarket Accessories
Do not connect aftermarket accessories into the following circuits:
CAUTION: Refer to SIR Service Precautions Caution In Cautions and Notices.
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SIR circuits, all such circuits are indicated on circuit diagrams with the SIR symbol.
NOTE: Refer to OBD II Symbol Description Notice in Cautions and Notices.
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OBD II circuits, all such circuits are indicated on circuit diagrams with the OBD II symbol.
Always check for aftermarket accessories (non-OEM) as the first step in diagnosing electrical problems. If the vehicle is so equipped, disconnect the
system to verify that these add-on accessories are not the cause of the problems.
Possible causes of vehicle problems related to aftermarket accessories include:
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Power feeds connected to points other than the battery.
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Antenna location.
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Transceiver wiring located too close to vehicle electronic modules or wiring.
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Poor shielding or poor connectors on antenna feed line.
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Check for recent service bulletins detailing installation guidelines for aftermarket accessories.
Intermittents and Poor Connections Diagnosis
Most intermittents are caused by faulty electrical connections or wiring. Inspect for the following items:
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Wiring broken inside the insulation.
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Poor connection between the male and female terminal at a connector. Refer to Testing for Proper Terminal Contact below for the specific
procedure.
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Poor terminal to wire connection. Some conditions which fall under this description are poor crimps, poor solder joints, crimping over wire the
insulation rather than the wire itself and corrosion in the wire to terminal contact area, etc.
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Wire insulation which is rubbed through. This causes an intermittent short as the bare area touches other wiring or parts of the vehicle.
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Refer to Testing for Electrical Intermittents for test procedures to detect intermittent open, high resistance, short to ground, and short to voltage
conditions. See: Diagrams/Diagnostic Aids
Testing for Proper Terminal Contact
It is important to test terminal contact at the component and any in-line connectors before replacing a suspect component. Mating terminals must
be inspected to ensure good terminal contact. A poor connection between the make and female terminal at a connector may be the result of
contamination or deformation.
Contamination may be caused by the connector halves being improperly connected. A missing or damaged connector seal, damage to the
connector itself, or exposing the terminals to moisture and dirt can also cause contamination. Contamination, usually in the underhood or
underbody connectors, leads to terminal corrosion, causing an open circuit or intermittently open circuit.
Deformation is caused by probing the mating side of a connector terminal without the proper adapter, improperly joining the connector halves, or
repeatedly separating and joining the connector halves. Deformation, usually to the female terminal contact tang, can result in poor terminal
contact causing an open or intermittently open circuit.
Round Wire Connectors
Follow the procedure below to test terminal contact of Metri-Pack or 56 series terminals. Refer to J 38125-B Terminal Repair Kit or the J
38125-4 Instruction Manual for terminal identification.
Follow the procedure below in order to test terminal contact.
1. Separate the connector halves.
2. Visually inspect the connector halves for contamination. Contamination may result in a white or green build-up within the connector body or
between terminals. This causes high terminal resistance, intermittent contact, or an open circuit. An underhood or underbody connector that
shows signs of contamination should be replaced in its entirety: terminals, seals, and connector body.
3. Using an equivalent male terminal from the J 38125-B, test that the retention force is significantly different between a good terminal and a
suspect terminal. Replace the female terminal in question.
Flat Wire (Dock and Lock) Connectors
