Cooling Off the Pre-heater and After-Glow - Transmission Digest

Cooling Off the Pre-heater and After-Glow

The Isuzu/GMC Forward Tiltmaster truck (otherwise known as the NPR/W4/4000) with a diesel engine and the JF506E transmission has a setup for recovering engine coolant that has been known to cause hard starting or a no-start condition. And it always seems to become a problem after the transmission needs repair; at least, that is what the customer says until you finally figure out what is the real cause of the problem.

Cooling Off the Pre-heater and After-Glow

Technically Speaking

Subject: Intrusion of engine coolant into fuse and relay box
Unit: JF506E
Essential Reading: Rebuilder, Diagnostician
Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

Technically Speaking

  • Subject: Intrusion of engine coolant into fuse and relay box
  • Unit: JF506E
  • Essential Reading: Rebuilder, Diagnostician
  • Author: Wayne Colonna, ATSG, Transmission Digest Technical Editor

The Isuzu/GMC Forward Tiltmaster truck (otherwise known as the NPR/W4/4000) with a diesel engine and the JF506E transmission has a setup for recovering engine coolant that has been known to cause hard starting or a no-start condition. And it always seems to become a problem after the transmission needs repair; at least, that is what the customer says until you finally figure out what is the real cause of the problem.

The reserve tank used to capture the expanded engine coolant is placed into a bracket and attached to the frame rail with an overflow hose that drips directly onto a relay box, as you can see in Figure 1. Inside this box are four relays: the exhaust-brake relay, the starter relay, and glow-plug relays 1 and 2 (see Figure 2).

I think the pictures are self explanatory, especially when you learn the function of each of the relays contained in the box. Of course, when the vehicle is new there is a cover on the box to protect the relays and the drip hose is bracketed, directing the dripping away from the box. But these trucks are worked hard, and in time the drip hose gets free from its bracket while the cover either is left off or falls off. As a result, the relays are subject to a sporadic dripping of water that can affect any one or a combination of these relays.

Obviously, if it is the starter relay we could have a no-start complaint. If the exhaust-brake relay fails there is no engine-braking assistance to the transmission, which could be the reason the transmission found its way into the shop for repair in the first place. If it is one or both of the glow-plug relays we could have a hard-start or no-start complaint. The glow-plug relays are controlled by the QOSIII controller to provide quick pre-heating, quick after-glow and after-glow operations. And there is nothing worse than getting both your pre-heat and after-glow cooled off with a little water! So if the customer tells you they never had a hard-start problem until you repaired the transmission, you will know he is all wet.

One other tip: If the glow-plug relays are compromised by a heavy dose of water intrusion, the No. 5 fuse, which is the power supply to the relays, will blow. That fuse is also the power supply to many of the indicator lights in the dash, and if it is blown these lights will not illuminate (see figures 3 and 4).

You May Also Like

Sherlock Holmes Approach to an AB60 No-Move Situation

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult.  Using scopes provides

ab60

The effectiveness in diagnosing automatic transmission malfunctions is an art form. Although there are similarities among the wide varieties of transmissions on the road, each transmission has its own peculiarities. Aside from having mechanical, hydraulic, and electrical hardware systems to contend with, software/programming issues and various vehicle platforms make diagnostics much more difficult. 

GM 6T40 Pump Identification Guide

The 6T40 was introduced in 2008 for General Motors front-wheel-drive cars in the Chevrolet Malibu and has gone through several changes throughout its three generations, specifically in the pump area. The 6T40 is closely related to the more lightweight 6T30 and the heavier duty 6T45 and 6T50. Generation one started phasing out during the 2012

Seeing the Forest AND the Trees

They say that the proverbial phrase “I couldn’t see the forest for the trees” means that a person or organization cannot see the big picture because it focuses too much on the details. Related Articles – 4L60E Harsh 1-2 Shift – TASC Force Tips: Diagnosing 8L45 & 8L90 Shift Complaints – TASC Force Tips: Hydraulics

The Manifold Pipeway

The Honda six-speed transmission has been on the bench of many specialty shops for one reason or another (figure 1). But, for those of you who have yet to lay your hands on one, mounted on the upper side of the unit is one of the largest, if not the largest solenoid and pressure switch

8L90 Vacuum Testing

Below are the diagrams for vacuum testing GM 8L90 transmissions. Note: OE valves are shown in rest position and should be tested in rest position unless otherwise indicated. Test locations are pointed to with an arrow. Springs are not shown for visual clarity. A low vacuum reading indicates wear. For specific vacuum test information, refer

Other Posts

Sometimes, a diagnostic code is all you need

With ATSG having the opportunity to help shops solve problems, sometimes we get faced with some real doozies. A shop will call and give us a laundry list of DTCs, leaving us to think someone must have a bulkhead connector unplugged. We then go through the arduous task of deciding which codes prompted other codes

10L80 and 10R80 pump gear differences

You may have seen an article in the August 2023 issue of Transmission Digest called “GM 10L80: A new kind of pump noise,” which goes over how the front cover housing in the 10L80 is fitted with a converter drive gear and idler gear. The idler gear drives the pump’s driven gear, and is press

Spotting different 68RFE designs through the years to avoid issues

The Chrysler 68RFE has had several changes through the years. Its four-speed predecessor began with a noisy solenoid pack identified by a black colored pass-through case connector (seen in Figure 1).  Related Articles – Going the extra mile: Proving your transmission repair suspicions – Diagnosing Ford 10R60, 10R80 and 10R140 series speed sensor issues – Jatco JF613E

Sometimes, you should sweat the small stuff

It’s a common phrase: There may have been a time when you worried about something, and someone who knew what you are going through said, “Hey, don’t sweat the small stuff.” Sometimes, this may be good advice. But other times, it may be wise to handle the small stuff before it becomes bigger “stuff.”  Related