I'm chasing a number of DTCs on our 2002 Jetta TDI (ALH engine, 3rd generation, late production, controls with 4-wire glow plugs). Most of the codes are from components that share a common power source the ECM Power Supply Relay (marked 109, called J317 if VW schematics) which is switched by the ECM when the key is turned on. We've also had leaks from the sunroof drain in the left (driver's) side A-pillar which means water gets close to the relay panel where the 109 relay is mounted.
So, I've been investigating that area and when I pulled the relay it was warm. It looked nice with no sign of water damage, but it was warm.
In the interest of actually understanding the problem I've been "playing" with the relay. Here's what I've found so far:
The coil resistance is about 145Ω when the relay is cold and about 165Ω after the coil has been energized for 30 minutes.
The coils pulls 62.1 mA.
After about 30 minutes with the coil energized, but no current on the switched contacts, with an ambient temperature of 18° C (measure with a K-type thermocouple on a DMM), I read a temperature of 25° C when the relay is sitting on the thermocouple which is sitting on my desk. By feel I might be able to tell that the case is warmer than ambient, but it is definitely cooler than it was when I pulled it from the car.
The resistance of the switched contacts is essentially unreadable - my DMM (Fluke model 73) shows 0.0Ω with an occasional reading of 0.1Ω. But, the loads on the relay are fused at 10 A, 30 A, and 10 A (ECM and injection pump, PCV heat, and engine control solenoids and the MAF sensor). At 50 A with a contact resistance of even 0.01Ω the power dissipation would be 25 W. That seems like enough heat to be a problem and enough to make the relay feel quite hot.
So, the questions:
How warm should a "normal" relay be, assuming a 100% duty cycle and a reasonably high current? I assume some heating from the coil could be normal, but corroded contacts would also produce heating and one explanation for the codes could be the relay dropping out.
Should I replace it, just because? They are cheap.
Codes for anybody who's interested:
17946 (P1538) - Fuel Shutoff Solenoid (N109) - 35-10 - Open or Short to Ground - Intermittent
17849 (P1441) - EGR Valve (N18) - 35-10 - Open Circuit or Short to Ground - Intermittent
19561 (P3105) - Valve for Intake Manifold Flap (N239) - 35-10 - Open or Short to Ground - Intermittent
16629 (P0245) - Solenoid Valve for Boost Pressure Control (N75) - 35-10 - Short to Ground - Intermittent
16600 (P0216) - Commencement of Injection Valve (N108) - 35-10 - Circuit Malfunction - Intermittent