[the following was submitted for inclusion in the 700-900 FAQ so check there for additional information and updates]

Procedures for dealing with suspected knock sensor problems for an LH 2.4 system with EZ116-K ignition. Tests for other systems will be similar. Check the wiring diagram for your particular model and year to verify connector pins and wire colors.

Knock sensor problems

o OBD ignition trouble code 1-4-2 "Missing signal from knock sensor"

--The ignition system control unit (ICU) isn't properly "seeing" the knock sensor.

o OBD fuel system trouble code 3-1-2 "Missing knock sensor signal"

--The fuel system control unit (FCU) isn't getting the knock sensor signal from the ignition unit (ICU) at start-up.

o Poor performance and acceleration due to excessively retarded timing

--Over-sensitive knock sensor possibly due to over-torqued or failed knock sensor.

o "Cheap" gas and heavily carboned engines may cause misfiring to the point that the knock sensor signal is not "believed" by the ECU.

Wiring and the knock sensor itself are by far the most common sources of knock sensor problems.

The knock sensor can only be tested dynamically for proper waveform output with an oscilloscope. Unless it makes you feel useful, there is no point in tapping on the block to simulate knock sensor activity. The voltage output of the piezoelectric quartz is too small and brief for normal measurement and, furthermore, the newer ignition systems won't be fooled into changing the timing as they selectively only detect knocking that would coincide with a misfire.

Start by making sure any engine diagnostic codes are for real by resetting the trouble codes (or disconnecting the battery) and wait to see if they reappear. Then do the physical and electrical checks below. If all other tests check out you may want to swap in a known good knock sensor on spec. Failing that an ICU swap may be in order. Only in desperation should the FCU be swapped on spec.

Physical checks

1. Check that the knock sensor (on the block, left side, down below intake runners #2 and #3) is properly connected to the wiring harness. It's easy to leave this connector off if you've been working on the engine.

2. Make sure the wiring connector for the knock sensor (green with black or brown wire) has not been accidentally switched with the block temp sensor connector (red/black with grey/white wire). The connectors are alike.

3. Make sure all connections are making good contact (straighten bent/separated contacts, check pins are fully seated by pushing in from back side). Remember to check the associated connector block at the strut tower or firewall. Make sure all connections are clean and protected from oxidation. Inspect for deteriorated/damaged wiring. Use an approved type of electrical contact cleaner. Squeeze dielectric grease into both sides of the connectors before re-assembly.

Electrical checks

Note that testing at the ECU connectors requires the use of a multi-meter and some skill in electronic/electrical testing. Accidents can be very expensive. To avoid connector damage, do not probe connectors from the end, probe only from the sides or back. When working with ECU modules and sensors, always keep the ignition OFF (KP0) and disable power to the electronic unit (by pulling all ECU fuses or disconnecting the battery) except when required during testing. This will help avoid accidental damage due to stray voltage or static discharge, especially when removing or replacing connectors.

1. At the ICU connector (EZ116-K, EZ117-K or RexI ignition control unit) check the wiring from the knock sensor.

a) Remove the knock sensor connector.

b) Remove the ICU connector and remove the shell to access the side of the connector for testing (note the pin numbers stamped on the connector).

c) Measure the resistance between ICU pin 12 and ground and between pin 13 and ground. Both should be infinite (open). Anything else indicates damaged/shorted wiring.

d) Place a jumper wire at the knock sensor connector (between pins 1 and 2).

e) Measure the resistance between ICU connector pins 12 and 13. It should be zero ohms. Infinite resistance indicates an open wire or bad connector. Anything else indicates a dirty connector.

2. At the FCU connector (LH 2.4 fuel injection control unit) check the knock sensor signal from the ICU (pin 4). Applies to EZ116-K ignition only.

a) Remove the FCU connector and remove the shell to access the side of the connector for testing (note the pin numbers stamped on the connector).

b) Re-install fuses. Turn the ignition to ON (KPII).

c) Measure the voltage between FCU connector pin 28 and ground. It should be approx +0.7 volts. Anything else indicates a problem with the ICU or its wiring.