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Cadillac and a Honda
This Honda Failure is Very Common
By Richard McCuistian Two different cars – two similar problems. 1995 Cadillac Deville 167,109 miles 4.6L Engine 4T60E Transaxle Won’t start unless sensor is unplugged...
Mental Gear Shifting
As a professional technician who’s logged a quarter of a century in the field, fighting my way through more than a few poorly written pinpoint tests and faultily drawn wiring schematics, my personal aim as an instructor is to produce entry level techs who can stand on their own two feet. I try to lay a solid knowledge foundation that they can build on, because we’re all students at heart. One good way to build ability into a new learner is to give him or her a problem to solve, point them at the shop manual and let them click their way through the forest of digital data so they’ll be able to function unsupervised in a twenty-first century shop.
In the service bay, as much as they might want to help, the TSB’s, neighborly online technicians, and hotline engineers too often run out of ideas, and woe unto us if we can’t punch past the book and find the problem with critical thinking and logical reasoning. The rub is that on a system we’re not accustomed to – even an older one—, we’re prone to make silly mistakes sometimes. At least I am!
Well, burgeoning techs aren’t accustomed to ANY system and it is expedient that they learn how to troubleshoot on their own. We all generally learn more struggling with a tough problem than we do when another technician steps in to spoon-feed us the answer. Be that as it may, we all need help sometimes, and getting the vehicle back to the customer in a timely fashion is important, to be sure. But let’s be ‘real’: we’ve all known technicians who just want to avoid getting their mental knuckles skinned and move on to the next gravy-saturated job ticket. Those guys couldn’t care less for the mind-bending, character-shaping experiences that come from having to get up close and personal with the hot potato concerns that don’t earn them any money, and some clock minutes on every time consuming diagnostic just can’t be billed.
Fruitlessly sifting through pinpoint tests and connector pinouts to ferret out an annoying glitch can be challenging or frustrating (or both), depending on pressure, priorities, and the temperament and/or resolve of the contender. And like Rocky preparing to face heavyweight champion Apollo Creed, every serious auto mechanics student needs to have faced tough opponents in training if they don’t want to have their fanny handed to them in the first round. The Case of the Abandoned Deville
This 1995 Sedan Deville wasn’t really abandoned; it was a spare car that had been sitting fallow for a few months because the owner (an instructor at our main campus) said it wouldn’t run unless he unplugged the Mass Airflow sensor, and even then it would barely run. I told him to bring it in and we’d have a look at it. Somehow the guy got it started and limped it over to the shop, but he told me it probably wouldn’t start again after he shut it off.
Victor saw the Cadillac sitting outside and asked for the job, so I aimed him at it with an OTC Genisys scan tool and a computer full of Alldata without even looking at the car myself.
Getting the cars fixed is secondary. Victor’s learning curve was of paramount importance, and this was one of those sink or swim situations.
One of the first things Victor discovered was that this Cadillac wasn’t equipped with a Mass Airflow Sensor; the owner had disconnected the Intake Air Temperature sensor, which may or may not have had anything to do with the owner getting the crippled Caddy started.
The second thing Victor discovered was that the car wouldn’t start for him with or without the sensor unplugged and besides that, it wouldn’t talk to the scan tool. This Cadillac is equipped with an OBD I system (some 1995 models have an OBD II DLC connector but in reality are OBD I) and while the Genisys led Victor through its selection screens to a point where it was supposed to talk to the Cadillac, it gave nothing but communication failure messages.
“Go to the shop manual and see what it tells you to do about communication problems.” I told him. It would be a great learning experience; just about every job requires the students to do shop manual research. He headed for one of the computers to point and click for awhile. Detour Through a Honda
On a concurrent note, I had checked a 1991 Honda Accord late one afternoon the previous week for a no-start (my students were all gone for the day) and found that there was no spark at the plug or from the coil. The distributor had power available and the camshaft was spinning it, so I knew the timing belt was intact.
The owner managed to gather some money and Michael, another one of my students replaced the distributor with a reman unit and set the timing. The old Honda was gone for a few days before the owner came trudging back into the shop; her car had failed to start again, but when we checked it this time, she had plenty of spark. She also had fuel injector operation, but she had no fuel pressure. Obviously, rather than throwing a pump at the Honda, we needed to find out why there was no pressure.
Michael went to the computer in search of whatever pertinent information he could find. The girl who owned the car probably thought she had purchased a distributor she didn’t need, but that couldn’t be helped; I knew better.
In the meantime, Victor was getting slapped around by the Cadillac; I always teach the guys to check uncooperative or inoperative electronic components for power and ground first, and Victor had determined that this one had the three necessary B+ feeds and four grounds it needed at the PCM, but it still wouldn’t talk to the scan tool, and the Class 2 data line wasn’t shorted or open between the PCM and the DLC.
“Before we condemn the PCM,” I told Victor, “let’s root around under the hood and see what we find the old fashioned way.” What I didn’t tell him was that I would have done that first.
Well, the 4.6L had a good 5 volt reference voltage at the TP sensor (a wise test to see if the PCM is at least partially powered up and grounded, the affirmative of which we already knew) and the 4.6 also had spark and fuel injector operation, but we discovered only ten pounds of fuel pressure at the test port.
Victor wondered aloud about the fuel filter, but I explained that a clogged fuel filter generally allows pressure even if it doesn’t allow volume, and while I know it’s theoretically possible, I’ve never personally seen a clogged inline fuel filter keep a fuel injected vehicle from starting. Besides, somebody had already changed the fuel filter in an apparent attempt to straighten this problem out, and it was hanging by the hoses in plain sight. That would need to be straightened out later. The Caddy Cranks Up A few years ago I bought a cheap A/C flush kit that consists of a pressure tank and a hose with a rubber tipped blower-style nozzle on the end for flushing A/C systems. With an old R12 A/C hose, we connected the can to the fuel rail, put about a pint of gasoline in it, and added about 50 lbs of shop air pressure to push the fuel past the injectors. The Caddy started and ran like a champ. The pump in the tank had plenty of voltage and unrestricted flow, but it just wasn’t doing the job. The replacement pump rung up at more than three Ben Franklins. Wasted Work? Not Really!
Curious as to why the Cadillac wouldn’t talk to the Genisys, I fetched the old Tech I scan tool (I sometimes forget I have it) from the tool room cage and connected it to the DLC. I worked my way through the menu to the datastream and was able to access everything when I realized that I could have used the built-in Cadillac scan tool that I had forgotten was there.
Duh! It would have been a simple matter to press “off” and “warmer” on the A/C head and access the codes and PIDs on the Message Center instead of fooling with all the tests I had Victor perform. Nevertheless, the work he did wasn’t wasted because he needed to understand the principles and procedures related to checking a no-communication concern. To a technician, a goofy boo-boo like this would have been a waste of time, but to a student, the experience was invaluable. It was kind of like snatching a gas tank to replace the pump only to look up and find that there was a handy fuel pump access plate under the seat. Ever been there? I have!
After the fuel pump replacement, the Cadillac ran like a charm, but the fuel gauge would never move off empty, even after we added ten gallons of gas. Disconnecting the harness from the tank should have driven the needle past full, but it didn’t. There was some sort of gauge or wiring problem, but the owner needed the car and already had sticker shock about the price of the fuel pump, so he took it like it was.
Back to the Honda
| Ford uses two separate relays for this job, calling one the “EEC power” relay (which supplies the injectors, fuel pump relay coil, PCM, and various solenoids with power). The Ford fuel pump relay drives the fuel pump. Chrysler uses what they call an Automatic Shut Down (ASD) relay to power up the fuel pump relay coil, the injectors, the ignition coil, and the generator field. For years GM used a fuel pump relay wired parallel with the oil pressure switch to drive the fuel pump; if the relay fails, the oil pressure switch completes the circuit to the fuel pump as long as oil pressure is present to control the switch. |
But what about the Accord? Michael had found the fuel pump part of the engine controls schematic, but when he returned to the car and turned the key, it started and ran just fine. He warmed the car up and shut it down, starting it several times before it failed to start again. We had an intermittently operating fuel pump.
The ‘Main Relay’ (present on most Asian imports) on this Honda actually contains two individual relays and is installed at the left side of passenger compartment behind the dash above the cruise control module, which must be removed in order to access it.
One of the unit’s internal relays is energized whenever the ignition is on, and it supplies battery voltage to the Engine controller, the injectors and to the second relay, which feeds power to the fuel pump and is energized for 2 seconds when the ignition is switched to the “on” position. The fuel pump relay will continue to run the pump if the starter is spinning or if the engine fires up, and it obviously supplies power to the fuel pump when the engine is running. What Michael discovered as he watched the fuel pressure and fiddled with the key was that sometimes the pump would run and sometimes it wouldn’t.
The relay has three power feeds, namely pin 7 (Yellow/Blue, always hot, feeding the common terminal on the Engine Controller relay), pin 5 (Black/Yellow, hot in “run,” feeding the common terminal on the Fuel Pump relay), and pin 2, (Black/Green, hot in “start” only, feeding a “start” signal to the relay). The Fuel Pump receives its power from the Yellow wire via pin 6. As it was, the relay coil was being energized by the PCM and there was always power at the Green/Black wire, but the relay wasn’t always sending power out to the pump from pin 6. It would never fail while the engine was running; it would simply fail to start. A $50 Main Relay from the local Honda dealer parts department put the Accord back in the wind.
Whatever Works!
There are a lot of fine people out there who just don’t have a lot of money to spend on their aging cars, yet owning an operable car (particularly in rural areas where public transportation is non-existent) is a matter of survival for most people, and so they do whatever works to keep their ride running until the car’s last wheeze. In my closing conversation with the Honda owner, she made mention of the fact that while the Accord had been intermittently cantankerous about starting for a few months, it never gave trouble once she got it going. She said she was accustomed to having to switch the key off and on amidst multiple attempts to get it fired up on occasion, and she had always been able to make it happen until the spark went away and the Honda didn’t respond.
The end result was that we fixed her second problem first (ignition) and her first problem (fuel pressure) reappeared, prompting her to return to the shop. What’s amazing is how many people I know who are naturally prone to do whatever they have to in order to drive a malady-stricken car for as long as they can without having it worked on. I remember hearing a woman on “Click and Clack” who always poured a little water in her console mounted ignition switch to get it to work, and she kept some water on hand just for that. Likewise, the Caddy owner was searching for a patch to his problem when he unplugged the IAT sensor.
R.W.M.
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Learning From My Experience 
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