Service slants

Motor,  Jun 2002  by Marcy, Thomas

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After completing the repair, roadtest the vehicle to make sure the condition has been corrected.

Jeep

Exhaust buzz. Some 2000 Cherokees may exhibit a buzzing or droning sound in the exhaust system, which is usually heard when engine speed hits 1700 to 2400 rpm. The sound may be heard while the vehicle is either rolling in Neutral or being driven with the tranny in gear.

To check things out, warm the engine, place the transmission in Park and raise engine speed to 1700 rpm. Then slowly raise the speed further, to 2400 rpm. If the sound remains, a revised muffler/tailpipe assembly (Part No. 05019872AA for MDH 0116XX and prior models, Part No. 52011262AH for MDH 0117XX and later models) should quell the noise.

Mazda

Rear tapping noise. Some 1998-- 2000 Mazda 626s en-At a tapping sound that can be heard coming from the rear of the vehicle within ten minutes after a cold start. According to Mazda, the noise may be coming from the CDCV (Canister Drain Cut Valve) solenoid during evap emissions monitoring. The noise may be difficult to duplicate under normal driving conditions, so Mazda advises keeping the vehicle at your shop overnight, if possible, so you can cold-start it the next morning to verify the complaint.

To check the valve, connect an NGS or equivalent scan tester to the DLC and select the Active Command Mode. Next, select the Evap PCV PID test and press "Start," then change the mode to "All Off." Press "Start" and "Stop" to cycle the CDCV solenoid valve on and off and listen for noise at the rear of the vehicle. If needed, you can repeat the test several times.

If you can confirm that the CDCV is the culprit, remove the nut securing it to the vehicle and remove the valve. Next, connect the CDCV to the threaded rubber insulator of a new bracket. Note, however, that before the CDCV is installed to the threaded rubber insulator, the insulator must be moved to the opposite side of the bracket. Attach the bracket and CDCV to the vehicle and repeat the test to confirm that the noise has been eliminated.

Ford

False low coolant indication. The Low Coolant lamp on some 1999-2000 Cougars may illuminate even though the coolant appears to be at a normal level. This may be caused by either a marginal coolant level, a defective coolant level sensor, a sticking float or defective sensor wiring.

Normally, the coolant lamp lights briefly as a self-test when the ignition key is first turned on. It should turn off after 5 seconds. The lamp then illuminates anytime a low-coolant-level signal arrives to the Hybrid Electronic Cluster (HEC) while the car is being driven. The HEC must sense this signal for longer than 33 seconds before the warning lamp will illuminate. This is to prevent normal coolant slosh from triggering the warning lamp. Anytime the lamp does go on after the 5-second period, the ignition key must be cycled again before the lamp will turn off.

Note that the electrical contacts in the low-coolant sensor are closed when the coolant level is in the normal range, meaning the warning lamp is off. The lamp turns on-meaning the switch contacts open-when the coolant drops below the MIN mark on the expansion tank. Remember, the sensor is not in direct contact with the coolant itself, but magnetically monitors the position of a float in the expansion tank.