Simple DSM testing procedures

These tests are generally as described in the 92 Laser/Talon service manual.
They are not guaranteed in any way whatsoever.

To the best of my knowledge, these tests should apply to 1st generation vehicles as noted
in each section. I believe that most of the tests should apply to the appropriate 2Gs as well.
If anybody has the correct info, please let me know

All tests are with the key in your pocket unless specifically stated otherwise.

Idle Stepper Control Motor (ISC Motor)

Testing Procedure: Test the resistance between the following pairs: (The spec is 28-33 ohms at 68F) 1-2 2-3 4-5 5-6

Symptoms: Any idle problem (high idle, low idle, stalling...) may be the result of a troubled ISC. If you have a sudden idle problem, this is a good place to start. Location: The ISC is located beneath the throttle body. It is light brown (on my car), and has a 6 pin connector. (On very early models, the ISC may be integral to the TB and located under the TPS).

Throttle Postition Sensor (TPS)

Testing Procedure: (1) Test the resistance between pins 1 and 4. The resistance should measure 3500 - 6500 ohms (2) Measure the resistance between pins 2 and 4 while rotating the throttle open. The resistance should change smoothly.

Symptoms: Location: The TPS is attached to the engine side of the throttle body

Engine Coolant Temperature Sensor

Note: There are 3 sensors in the thermostat housing: The A/C temp sensor is in the upper half of the thermostat housing The instrument cluster temp sensor is the smaller single wire tap The ECU temp sensor is lowest in the thermostat housing and points slightly downwards.

Symptoms: If the ECU determines the sensor has failed, the failsafe function is to assume the car is warmed up. This should also cause a diag code of 21. If the ECU does not notice that the sensor has failed, it will remain in 'warm up mode'. This will cause the car to idle high even when warm, and may affect fuel mileage (for the worse). Location: In the thermostat housing Testing Procedure: The service manual describes a procedure of removing the sensor, testing it in a tub of heated water with a thermostat, etc. This is way to much work, and requires sealent to reinstall, etc. I think it's probably sufficient to test the resistance with the car cold and leave it at that. You could also (at your own risk) test the resistance after the car has been warmed up. Here is the appropriate data: Temp (C/F) K-Ohms 0/32 5.9 20/68 2.5 40/104 2.7 80/176 0.3 This chart is wrong! However, it is what is shown in my service manual. I believe that the resistance at 20/68 is a typo and should be 3.5. If somebody else has a service manual that is correct, please let me know

Idle Position Switch

Symptoms: Typically the switch is going to fail in a 'permanently open' state which does not seem to cause any obvious symptoms. (If you have an A/F, you may see the ECU fail to shutdown the injectors during coasting.) At least in one case, the switch failed 'permanently closed'... this seemed to prevent the ECU from dropping into idle mode, causing it to leave the ISC wide open, leaving the car with an abnormally high idle. Location: located behind the throttle body, in line with the throttle cable (look for the black rubber boot) Testing Procedure: Remove the booty, and test for continuity between the switch terminal and ground while manipulating the throttle cable. The circuit should show continuity (closed circuit) when throttle is fully closed, and open circuit when the throttle is open at all. Note: Be careful to get the terminal into the plug when reconnecting it. It doesn't have a real positive feel or alignment, so it's easy to miss to connection.

Oxygen Sensor

Location: The wire that runs over the upper heat shield in front of the engine is for the O2 sensor. One end is the O2 sensor. The other way leads to the (more important) connector, which is located under the thermostat housing.

Symptoms: There are three ways for the O2 sensor to fail: (1) If it dies totally, the ECU will give a code 11 (2) The exhaust grounding strap can become a problem. This is a very common failure which causes bad mileage due to the car running 'rich'. I'm working on a test for this condition. (3) The sensor can become 'slow'. This seems to happen to all O2 sensors over time, and diagnosis is a judgement call. Testing Procedure: Test connector pins 3-4 for a resistance of 12 ohms at 68F. (This is the heating coil) The service manual specifies a second test which I won't repeat here. A better method is to read the O2 sensor voltage from the test port (preferably using an analog VOM.) Check the digest archives for more info.

Injectors

Symptoms: I think it's more likely that an injector will be clogged rather than dead, which makes this resistance test just about useless. A clogged injector causes the fuel not to be distributed evenly, potentially causing bad mileage, power loss, etc. Location: In between the fuel rail and the valve cover Testing Procedure: Test resistance. Resistance should be 2-3 ohms for Turbo, 13-16 ohms for non-turbo & 1.8L (all at 68F).

Solenoids

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Location: Boost Control Solenoid (BCS): mounted on the aircan Purge Control Solenoid: firewall mount, position #1 EGR Control Solenoid: firewall position #3 (only on CA cars) Fuel Pressure Control Solenoid: firewall position #2 Symptoms: BCS: stock vehicle shows 7-8 psi PCS: ?? EGR: Emissions problems FPCS: Warm start problems? Testing Procedure: Resistance across terminals should be 36-46 ohms (at 68F)

Intake Air Temperature Sensor

Turbo

Symptoms: ? Location: Aircan integral connector Testing Procedure: Test resistance between terminals as shown: Turbo: pins 6-8 Non-Turbo: pins 4-6 Temp (C/F) Ohms 0/32 6.0 20/68 2.7 80/176 0.4

Non-Turbo (2.0L and 1.8L)

Crank Angle Sensor/TDC Sensor

Location: This seems to be a single sensor (or at least 2 integral sensors). It is a hockey puck shaped unit located on the end of the intake cam behind the thermostat. Testing Procedure: There doesn't appear to be a test listed in my service manual. The two occurence I have heard of indicate that this is a critical faliure. This should be very easy for the ECU to flag, but that assumes that the car will run...

Alternator

Location: The alternator is located on the front right of the engine under the power steering pump. Symptoms: When the brake, coolant (the birdcage) and ? warning lights all come on at the same time, it's probably the alternator. Testing Procedure: The service manual lists the standard alternator tests. I personally say: pull it out and take it to Autozone.

More to come....