Engines With One Knock Sensor

CIS Turbo ECU Harness Connector (Pin # Locations):

There is no static test for a knock sensor, however there are ways of determining whether or not a knock sensor is working.

1. If the engine "pings" but code 2141 is NOT present, chances are the knock sensor is faulty or there is an open or shorted circuit between the sensor and the ECU. In this case there should also be a code 2142 (no signal from knock sensor). Check for open or grounded circuit between knock sensor connector terminal #2 and ECU terminal #15. Also check for open circuit between knock sensor connector terminal #1 and ECU terminal #16, &/or damaged shielding around knock sensor leads. If no wiring problems are found, replace the knock sensor.

2. If the engine pings and code 2141 is present, the knock sensor is probably OK, and there is a mechanical condition causing the noise and the code, such as excessive carbon deposits in the combustion chamber, overheating, incorrect distributor basic adjustment, or just poor quality gasoline.

NOTE: Turbo charger boost pressure is also controlled in part by the signal from the knock sensor. If the boost pressure is too great (inoperative wastegate or wastegate control), the ECU may not be able to eliminate knocking by retarding the timing. In this case, the knocking occurs mostly at high engine speeds and loads and can cause damage to pistons, rings, valves and spark plugs. If you suspect the boost pressure is too great and may be causing a knock, see also MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR in this section. If there is an overboost problem, check wastegate for sticking or binding and see WASTEGATE FREQUENCY VALVE in this section.

3. If the engine lacks power and code 2141 is present, even though the engine may not ping, the knock sensor is probably loose or has failed, and is signaling a knock when no knock has actually occurred. This causes the ECU to retard ignition timing unnecessarily, causing a significant power loss and possibly overheating.

DYNAMIC TEST

Typical Knock Sensor Signal:

The knock sensor can be tested dynamically with the use of an oscilloscope. With the ignition on, the sensor will produce a static wave pulse when a knock occurs. The wave pattern should look similar to that shown in the diagram, and can be observed on a scope by probing terminals #1 and #2 of the sensor connector while tapping on the engine block, near the sensor, with a small hammer or wrench. If there is a great deal of static from the sensor, the ECU may not be able to distinguish between the static and an actual knock, and continue retarding the timing unnecessarily.