|Carl’s Corner – Auto Repair Help|
|DIAGNOSE – THE TURN SIGNALS DON’T WORK OR DON’T WORK PROPERLY Part 2
By Reiner B.
Continued from Part 1
TURN SIGNAL REPAIR TIPS & TRICKS
One of the most common issues with turn signals is short circuits between live contacts and ground, or other circuits. When this happens, you are likely to either see a brake or head light bulb flash along with the turn indicator bulb when the turn signals are turned on, or the turn signal bulb lighting up when the brakes are activated or the headlights are turned on.
While these types of short circuits do happen on cars and SUV’s, it is more common on pick-up trucks, and particularly on trucks that see a lot of off-road use since the rear light clusters and wiring on these vehicles are not as well protected as the wiring on other types of vehicles are. However, since the same issues that affect pick-up trucks affect cars and SUV’s as well, the simple diagnostic steps outlined here should resolve the issue nine times out of every ten, regardless of the vehicle type.
NOTE #1: Note that to diagnose inoperable turn signals you may need to have access to a repair manual that includes a wiring diagram for the affected application. If a repair manual is not available, a suitable wiring diagram can often be found free of charge with an online search. Note that you will also require a good quality digital multimeter; simple test lights are mostly useless since they cannot measure electrical resistances in circuits accurately.
NOTE #2: As with all car troubles, approaching the issue of defective turn signals in a logical manner saves time and prevents misdiagnoses, so start the process with asking yourself the following questions, starting with-
Are all the turn signal bulbs affected?
NOTE: Some types of turn signal relay failures can cause all the turn signal bulbs to illuminate, but not to flash. While there are other causes of this, in the vast majority of cases a replacement of the turn signal relay with an OEM replacement part will resolve the issue.
Are only some turn signal bulbs affected?
If only some bulbs are affected, it is important to check if the affected bulb is only illuminating weakly, or if it is well and truly dead, since weak illumination can indicate a short circuit. Here is what to look for-
Are all the bulbs on only one side of the vehicle working?
If this is the case, suspect either a defective turn signal switch, or a defective turn signal relay. If replacing the turn signal relay does not fix the problem, replace the turn signal switch but be aware that removal of the steering wheel may be required, which could trigger the steering wheel (or other airbag(s)).
WARNING: If a defective turn signal switch is suspected, the better option is to refer the vehicle to the dealer or other competent repair shop for professional assistance, since triggering an airbag unexpectedly can cause serious personal injury.
Is the affected bulb not illuminating at all?
Is the replacement bulb still not illuminating?
If the bulb does not illuminate and multimeter shows the correct current on the live contact (as per the steps above), test the ground circuit between the outer metal part of the bulb holder and a known live wire that does not feed a turn signal. If the bulb holder is grounded properly, the multimeter will show a constant current; if there is no ground, the multimeter will show an open circuit. Finding and repairing the open ground circuit will resolve the problem, provided that the bulb is good, and that there is proper contact between the bulb and its holder.
Is the affected turn signal bulb illuminating weakly?
Are the turn signals flashing too fast / too slowly?
Since turn signal relays generally depend on a resistance spike to act as a trigger to switch between “ON” and “”OFF” states to cause the bulbs to flash, an excessive resistance will cause the bulbs to flash to slowly, while an insufficient resistance will cause the bulbs to flash too fast.
Typical causes of turn signals flashing to slowly include-
Typical causes of turn signals flashing too fast include-
Fixing an incorrect flash rate usually involves verifying that all bulbs are rated for the vehicle, and finding/repairing short circuits and/or abnormal electrical resistances. Also, note that the resistance of the indicating light on the dashboard is included in the total resistance of the turn signal circuit, so if the light on the dashboard blows, the flash rate of the turn signals is also affected.
NOTE: Note that one or more of the causes listed above can also cause the turn signals to illuminate, but not to flash on some applications. Be aware however, that distinguishing between a defective turn signal relay and other issues that cause turn signals not to flash can be tricky, and it is recommended that if the steps in this guide do not resolve the issue, the better option would be to refer the vehicle to a competent repair facility for professional diagnosis and repair.
Are other bulbs illuminating along with the turn signal?
Are some turn signals illuminating at times even when the turn signal switch is “OFF”?
This can happen if there is a short circuit the connector of the affected light cluster, or in the wiring harness that feeds power to one or more light clusters. Depending on the site and severity of the short circuit, applying the brakes, turning on the headlights, or engaging reverse gear can illuminate not only turn signal bulb, but also all the bulbs in a light cluster. Note though that this type of short circuit will not always cause one or more fuses to blow, and the remedy sometimes involves replacing the relevant wiring harness, as opposed to attempting repairs, which is sometimes made difficult by the routing of this harness on many vehicles.