Engine/Transmission (1998.5 - 2002) Another Grid Heater issue

[Darrenf]

Hey all,

I've read nearly all the posts on Grid Heater and am still having issues. I put in two new Stanco Relays, they seem to engage as they're supposed to but I don't get the voltage drop on dash voltmeter and no dimming of the dome light. I disconneted the ground wire at the intake horn and measure a voltage coming though the grids. I've gone so far as to even direct connect a jumper cable from the battery to the positive end of the grid and the under hood light didn't dim either. I've not read where anyone actually replaced the grid heaters, even after a sticky relay where you'd think the grid might burn up. Can the fusible link still carry voltage but not enough current?



Ideas/Suggestions.

 

[SGevers]

Stlll sounds like you either have a bad ground or a open in the hot somewhere.

 

[Sticks]

Stlll sounds like you either have a bad ground or a open in the hot somewhere.

If he has run a jumper direct to the grid heater and (dimming light is not the best indicator) no change, that leaves a bad ground, and that is rare if bolted down.



First, check your fuses. Next, check the heater terminals for voltage while the truck is cycling the heater. A simple test light will work if you don't have a volt meter. Same with the relays. Possible that the slip on connectors for the signal line and senor line are not making contact. You can also hook a jumper wire to the relay's signal terminal and manually cycle the heater instead of having to go back and forth to the ignition.



IIRC there is a code that will set in the PCU/ECU for a bad grid heater circuit.



My advice, if you want to verify the operation of the heater by itself, take the entire unit off the truck, and jumper both the positive and ground to a battery. I'd use an infrared thermometer or sprinkle a little water on the grid (should dry quickly or steam) and check for operation that way.

 

[Darrenf]

What was bothering me pretty bad was that I never could get 12volts coming off the engaged relays or at the positive side of the grid heater, but then as I thought about it, I'm not sure I would see 12v since the circuit is pretty much a short to ground on the other side of the heater. The short is what causes the the grid to heat, right? (kinduva a big resitor? Is there supposed to be resistance through the grid heater?) I only get 12 volts if I disconnect the gnd wire from the negative side of grid heater, so i know the relays are working.

I'll remove the heater from the truck today and see if i get the heater to even heat with just batteries and jumper cables.



Thanks for the responses.

 

[Darrenf]

Well... after pulling out the grid heater and hooking it up directly to the battery it was determined that there was nothing wrong the heater... nice and hot! So the problem had to be in the wires somewhere. Pulled out the fusible link and upon closer inspection it looked like the battery side ring lug might need some help didn't look that bad. So, cut off the old ring lug, soldered a new one on and... Viola!



Moral(s) of the story:

1. I hate battery corrosion

2. Don't underestimate the appearance of any terminal connected to the battery!

 

[Sticks]

What was bothering me pretty bad was that I never could get 12volts coming off the engaged relays or at the positive side of the grid heater...

That is called "Voltage Drop" and it is a way to determine/diagnose electrical issues. Hard for me to explain in words how to do it and how it works w/o visual aids.



It will identify broken wires, corrosion, weak connections and so on.



Glad you were able to identify your problem.

 

[Bob Cochran]

Think of it this way. If you measure across something and it has resistance there will be a VOLTAGE drop. No resistance no voltage drop. if you have two things with resistance in a circuit each will drop voltage in proportion to there resistance and if the voltage drops summed they will equal the supplied voltage. These is what happens on devices in series. Devices parallel it is lightly different explanation for another time with a white board!!!

 

[Sticks]

Think of it this way. If you measure across something and it has resistance there will be a VOLTAGE drop. No resistance no voltage drop. if you have two things with resistance in a circuit each will drop voltage in proportion to there resistance and if the voltage drops summed they will equal the supplied voltage. These is what happens on devices in series. Devices parallel it is lightly different explanation for another time with a white board!!!

READ - In a properly functioning circuit, there should be less than 500mv Voltage Drop BEFORE the load (Grid Heater in your case) with the positive lead of the voltmeter on the + terminal of the battery, and the negative lead on the +side of the load (Grid Heater terminal) during circuit operation to test for problems before the load. Same theory applies to testing alternators, starters and so forth. Application applies to the ground side as well so long as the + lead of the voltmeter is still placed closest to the + side of the circuit. Place the leads on both sides of the load to test for function of load... need visual aids now.